(Pocket-lint) - Things change quickly in the smartphone world and what was once a company's flagship, becomes supposedly second best as it makes way for the latest and greatest.

With the Apple iPhone 7 now on the shelves, what of the iPhone 6S? Is the 2015 flagship from Apple still worth considering given that Apple now offers a higher spec model?

At the launch of the iPhone 6S and iPhone 6S Plus on the 9 September 2015, Apple said that "the only thing that's changed is everything" and having used the iPhone 6s for a full year, it was right.

Virtually identical design to the iPhone 6

Now comes in Rose Gold

On the surface everything about the iPhone 6S appears the same as the earlier iPhone 6. The form is the familiar finish, complete with curved glass, curved edges, and a polished exterior. But if you read the specs then you'll see the two devices are ever so slightly different: the iPhone 6S measures 138.3 x 67.1 by 7.1mm and weighs 143g compared to the older iPhone 6 which measures 138.1 x 67.0 x 6.9mm and weighs 129g.

So the 6S is heavier and a tiny amount larger, but in the real world you'll be hard pushed to notice the difference in size or weight, we certainly haven't over the last year. If you are worried these tiny changes are going to mean your cases and accessories don't fit anymore, then don't be - we've had no trouble with a range of iPhone 6 accessories we've got in the office.

Apple won't confirm why the iPhone 6S has 14g of extra weight, but the belief is that it's a by-product of the new 3D Touch display (more on that in a bit) and the new stronger aluminium used for the casing (they aren't going to fall foul of bendgate again). The screen delivers the same 750 x 1336 resolution 4.7-inch panel as seen in the iPhone 6.

The other more pronounced change is the option to have the iPhone 6S in a Rose Gold finish, or "bros gold" as we like to call it. Oh, and it's no longer possible to get the iPhone 6 in a Gold finish, which is reserved for the 6S alone. If you're a man, the Rose Gold will get you comments, and it can at times look overly pink, but like a good glass of rose wine, it's soft and whimsical.

So the changes are there, but they don't impact the user experience. The iPhone 6S still looks as good as it did last year, which is a testament to Apple's design approach. Sure, some will moan that the camera protrudes slightly from the rear of the phone, but having used an iPhone 6 for the previous 12 months and now the 6S for the last 12 months, we've not found it to cause too many issues. Besides, Samsung and other manufacturers follow a similar suit with protruding cameras, so while we'd prefer a flush rear the design has almost become the norm across the board.

New pressure sensitive screen for additional commands

One of the biggest changes to how you use the iPhone 6S is the introduction of a new feature called 3D Touch. Working in a similar way to Force Touch on the Apple Watch and MacBook trackpad, the iPhone 6S can now determine how much pressure you place on the screen.

Baked into the core of iOS 9 and iOS 10 - the operating system that ships with the device - and available to third-party app developers, the 3D Touch feature opens a host of new options for users to get to information quickly. On the homescreen, for example, pressing down on certain icons now reveals a secondary level of options. Press on the Phone app icon and after a small haptic buzz the screen reveals your top three favourites to call. Do the same to the camera app icon and you get shortcuts - or as Apple calls them Quick Actions - to elements within the camera like Take Selfie or Record Slo-mo. Different apps provide different Quick Actions: Messages dynamically change based on who you are texting, while we love the Photos option that lets you quickly jump to photos you look a year ago.

But it's not just secondary menus on the homepage. The 3D Touch feature goes further in other ways, with Peek and Pop the primary example. This feature lets you peek into things, such as an email to see what it says without fully opening it, while the pop element is a longer press that then opens what you've been peeking into. This works particularly well for quickly glancing into a specific emails from your inbox, while being able to check your calendar to see if you are free - no need to go through the process of opening your calendar app and then double clicking the home button to return to the Mail app. The one we've been using the most, though, is the ability to press on the small Contacts icon within Messages and Mail to quickly access their details.

As 3D Touch can sense pressure levels, it's also come in handy when sketching in Notes and using the new Markup feature in Mail.

While 3D Touch is very clever and has the potential to add plenty to the experience, we've found over the last 12 months we've failed to really use it effectively. It's nice for deep pressing to get Wi-Fi, Bluetooth, or Battery menus from the settings icon, but we've found we've hardly used peek and pop, or other features at all. That might be different for you, but developers have struggled to get to grips using it, and we suspect users have struggled to remember it's there.

The one gesture we've constantly found hardest to perform or remember is the one where pressing on the edge of the screen brings up the app switch menu (usually a double-tap on the home button), which sometimes works, but other times doesn't - probably to do with how we are holding the 6S at the time. Other times we find ourselves cursing ourself when we've forgotten to use the feature altogether, until we forgot to even curse.

12 megapixel rear sensor

5 megapixel front camera

4k video support

While the two cameras on the iPhone 6S look the same as those on the iPhone 6 from the outside, both rear-facing and front-facing cameras have been improved. The rear camera now uses a 12-megapixel sensor, up from 8 megapixels, and comes with the usual Apple tweaks to get the most from the scene in front of you.

Photos are natural in their colours and tones, with the iPhone 6S performing as well as many compact cameras we've seen. In terms of performance, it's able to cope well with a multitude of different shots.

We're impressed with the autofocus too - it actually focuses on the subject, rather than trying to make the whole scene sharp - and copes with an array of lighting scenarios including low-light.

Although the default camera app doesn't allow you granular control over things like white balance and ISO levels, there are plenty of third-party apps that allow you to do just that.

On the front the 6S has a 5-megapixel iSight camera, but most important is a new feature that turns the entire phone screen into a sort of flash for those perfect selfies. Press the shutter button and the phone will analyse the light needed and then change the hue of the white accordingly. We've seen bright clean whites to creamy tones depending on the ambient light situation.

The improvements on the iPhone 6S over the iPhone 6 can be clearly seen, and Apple has continued to move the capabilities of the camera forward in its latest. Shots aren't just bigger in terms of output size, they're better as a result of all those additional tweaks.

Other camera advancements include bigger panoramas that capture even more detail. The main absence is a lack of optical image stabilisation, which the larger iPhone 6S Plus offers, and the more recent iPhone 7.

According to Apple, the problem with still photos is that they don't show what's happening at the time you take the photo. That laugh seconds before or after a magic moment, or the movement in the background of a river or waterfall. Its answer is something it calls Live Photos, which work by taking 1.5 seconds of video before and after the shot to give you a sense of movement to your photos.

Thing is, it's not exactly a brand new feature in the tech world. Look back to Cinemagraph from Nokia, or HTC Zoe, and you'll find similar solutions (ones that aren't talked about much at all these days).

Using the iPhone 6S a spilt second of that captured movement is shown every time you scroll through your images in the Photos app, while a press of the screen using 3D Touch lets you play the whole Live Photo clip.

The iPhone 6S and the 6S Plus are the only two Apple phones that can capture these Live Photos, but it's possible to share them with other iOS 9 and Mac OS X El Capitan users and keep the effect in place. But sending to Android and friends on other platforms won't work - they'll just receive a default still photo instead.

One frustration is that audio is automatically recorded, which at times is lovely - a child's giggle for example - but not so great when you've got the same child screaming in the background.

The people we've shown Live Photos to have fallen into two camps: those with kids and those without. Parents automatically get it and love it. Others, at the moment, not so much, but of the thousands of iPhone Live Photo shots we've taken since the launch of the iPhone 6S there have been some gems that we wouldn't have captured otherwise. A cheeky smile, a firework exploding in the air.

Sometimes though, we found that the Live Photo captured a better image, but the final one wasn't so great. It would be good to be able to pick any moment within that 1.5 seconds.

All that extra video adds to their size too, with a Live Photo being around two still photos in terms of storage. While you can offload some of that to Apple's iCloud Drive service (at a yearly subscription) a 16GB iPhone 6S isn't going to stretch as far as it used to (compounding the argument for a 32GB minimum model).

It's not just still photographs that have had an enhancement. New to the iPhone 6S is the ability to shoot 4K video, although you'll have to make sure you turn on the setting buried deep within the Settings app before you start shooting, as oddly it's not possible to do so from within the Camera app. Perhaps that's because 4K is a bit of a space-eater: a minute of 4K footage we shot came in at 375MB compared to 60MB for a 720p HD clip of the same length, so about six times larger.

Although 4K is very much in its infancy, that is changing fast with the price of 4K UHD TVs coming down and more content becoming available every month (Amazon has just announced the 4K-ready Fire TV with hundreds of 4K TV shows and movies).

The iPhone 6S doesn't feature a 4K screen like the Sony Xperia Z5 Premium, and you can't you stream its content to your television at this resolution via the new Apple TV (that doesn't support 4K either). But that hasn't stopped Apple from being ready when things do start to upgrade around you. While you do wait, you can use the 4K capture to zoom in on the footage you've shot if you want.

Quality is decent. The 3840 x 2160 footage is captured at 30fps, offering smooth playback, but there's no option for slow-motion capture at this higher resolution. If you want to use Slow-mo then that's available at 1080p 120fps and 720p 240fps for smooth playback at up to an eighth of the original speed.

Thanks to Clodge at C S Lewis in Ascot for allowing us to film.

The iPhone 6S now comes with iOS 10 bringing with it a number of new features above iOS 9 that the iPhone 6S launched with. This new software experience is a subtle change over what users will have seen in iOS 9. iOS 10 comes with a number of new features like a dedicated Home app to allow you to control and manage your HomeKit accessories, a much more advanced Messages app that bring things like apps and stickers, and Widgets to the lock screen so you can quickly grab information snippets from your favourite apps (if they are supported).

READ: Apple iOS 10 review: Bringing more complexity and features to your iPhone and iPad

The notion that iOS is a simple operating system is now a long and distant memory, given the complexity it opens up for power users. In iOS 10 Apple has focused on layering the experience with even more complexity and depth than ever before. In the same breath, if you're not a phone geek it's still a breeze to use. The update works well on the iPhone 6S. Giving a new lease of life to the 2015 flagship handset.

Low Power Mode

You would expect all these new features to hammer the battery, but they don't. Apple has not only improved the battery performance with iOS 9, but despite a 5 per cent dip in battery capacity compared to the iPhone 6, we've seen comparable life per charge.

One thing that will help the iPhone 6S last longer than the previous iPhone is the introduction of Low Power Mode. Available to all iPhones running iOS 9 rather than a specific new feature of the 6S, the new mode shuts down all non-essential functions to extend the battery life of the phone. You're asked if you want to turn the Low Power Mode on with 20 per cent remaining and again at the 10 per cent mark, giving you plenty of juice to still be able to order that Uber home at the end of the evening.

In our tests we've been really impressed with longevity. Our iPhone 6S used only 15 per cent of battery in 12 hours with it on, while an iPhone 6S Plus lasted a similar 24 hours for 29 per cent of battery. As ever with a phone, hammer it with the gaming apps and you'll squeeze that juice out faster, but it's all relative.

As a heavy user it won't last you till bedtime on a single charge, especially if you are travelling, so it's advisable for long days to pack a battery charger or a cable to be able to top up at some point.

A9 processor

Up to 240 hours standby, 14 hours of talk time

Apple boosted the power of the iPhone 6S, thus making it faster than the iPhone 6 and the iPad Air 2 as well, and while that has now be superseded by the iPhone 7 it is still a very capable device in terms of performance. There is an updated processor from the iPhone 6, more RAM, and other advances on the speed, efficiency, and technology front.

The motion (co) processor has now been incorporated into the main processor, dubbed the A9, to save power and increase performance, and for the time we've being using the 6S everything has run smoothly and swiftly.

Whether that's editing 4K video on the iPhone with iMovie, or playing graphically demanding games like Real Racing 3 or Asphalt 8 (it still gets a little hot after a while), we've not noticed any lag or latency issues. To the point: the iPhone 6S works.

Touch ID fans will also be pleased to hear the sensor has been upgraded too: it's a lot quicker to respond, although Apple still hasn't been able to solve the issue of not being able to use it with sweaty hands after running or wet fingertips after getting caught in the rain, something we've consistently been frustrated with over the last year, especially coming back from a run.

The iPhone 7 brings a number of changes to the party over the iPhone 6S, although the changes to the 2016 model aren't as pronounced as previous updates. Some will even say that by losing the headphone jack and having to use a dongle for headphones with a 3.5mm cable you are taking a step backwards.

However the iPhone 7 does bring an improved home button, a refinement on the design and a faster processor which aside from allowing apps to load faster, also helps with making the TouchID sensor respond faster amongst other things.

You can read more on how the two phones compare in our Apple iPhone 7 vs iPhone 6S vs iPhone 6: What's the difference? feature. If you can afford the iPhone 7, there is plenty on offer, but by opting for the iPhone 6S, you are still getting a very good phone.

Verdict An iPhone S update year usually means a couple of new features that most people could take or leave, but the iPhone 6S is the most exciting S model for a long time. It bucks the usual trend, delivering a phone that will offer plenty to iPhone users new and old alike. In practice the Touch 3D element has proved to be a gimmick that we could easily live without though. Improved battery life, enhanced cameras, slick operability from iOS 10 all make the iPhone 6S great to use, even if the screen resolution is still behind the current flagship curve. The addition of Live Photos, 4K video and baked-in Hey Siri might be less integral to all, but they're the kind of fun features people want and that Apple delivers well. While the new iPhone 7 offers a waterproof design, ditches the physical home button, and of course controversially, the headphone jack, there is still plenty to enjoy and like with the iPhone 6S making it a good handset for those that want Apple, but can't afford the top of the range flagship 2016 handset. For iPhone 5S readers looking to upgrade you'll move leaps and bounds ahead of what you've come to expect from your phone, while even keen iPhone 6 users will see benefits too. The iPhone 6S doesn't disappoint. Best smartphones 2020: The top mobile phones available to buy today The Apple iPhone 6S was first reviewed on 22 September 2015

Writing by Stuart Miles.