Project Svelte

Google refers to KitKat internally as Project Svelte, and for good reason: Performance optimization is the name of the game, and indeed, the operating system and preloaded apps have been trimmed down substantially in size. Android is leaner and meaner, and performance is quicker, making Android 4.4 more efficient for lower-end devices that don't have the same powerful internals as flagship devices. In particular, KitKat is meant for devices with at least 512MB of RAM onboard.

Developers can tweak their apps with a few lines of code to detect when a low-powered device is being used; when this happens, the app can be programmed to use fewer graphics and cut down on animations, transitions and other aspects that tend to drag down the app's performance. This is all part of Google's mission to bring Android to the "next billion devices" -- i.e., users in emerging markets.

Curiously, this newfound focus on the low-end part of the market only seems to serve manufacturers who are working on new phones that have yet to be released; most existing devices with 512MB of RAM aren't getting listed as candidates for receiving Android 4.4. We'd love to see how some older (and now irrelevant) devices would fare on the new OS, but we'll simply have to wait for someone to find a way to make it happen.

User interface

After booting up KitKat for the first time, you'll find the home screen still feels like the same old Android we know and love. But it isn't completely identical. The icons have been made a little larger to accommodate the additional screen real estate on bigger smartphones (although we noticed that many third-party app icons are a little fuzzy as a result). Google has also chosen to use a condensed version of Roboto for the home screen and app menu fonts. It fits in quite well here, but we doubt it would look as good integrated into other parts of the user experience.

You start off with only one home panel, but it can be expanded to include as many panels as you want -- we made it to 22 before giving up. Go into the app menu and you'll notice a couple drastic differences: There's wallpaper underneath the grid of icons now, rather than a pure black background, and the widget section is completely MIA. You'll find the latter by doing a long-press of the home screen, which now takes you to a screen where you can rearrange panels and change wallpaper in addition to satisfying your need for widgets.

It may be so subtle that you don't even realize it at first, but the status bar and navigation bar are no longer solid black on the home screen and app menu -- they're translucent, clearly showing off the wallpaper underneath. This is part of Google's new firmware design strategy: KitKat enables developers to completely hide these two bars, so that users can take full advantage of the extra screen space. We believe this will be incredibly useful in games and e-book apps, but this is only a small number of possible use cases.

The lock screen is largely the same as Android 4.3, but there are a few enhancements to the lock screen widgets. Most notable, however, is the new camera button on the lower-right corner of the screen; drag this up and to the left, and you're immediately into your camera app. We can't say that this is an improvement over the last version, since all we have to do on 4.3 is swipe to the left of the lock screen to access the viewfinder. Strangely, the button is placed in the same location as it is on iOS. Coincidence? You be the judge.

Google Now

Google Now was introduced with the first Jelly Bean update as part of Project Butter, and it's grown considerably ever since. There's a lot of momentum pushing it forward, and Android 4.4 only serves to increase its usefulness exponentially. One of those areas in which it's become more helpful is its integration into the Google Experience Launcher. Turn the Google Now feature on and you'll be whisked into the standard Google Now panel as soon as you swipe to the right from the main home panel.

Even though Google insists that Motorola still acts as its own company, it clearly didn't have any qualms about using the flagship Moto X for inspiration. In particular, the Nexus 5 has been bestowed with touchless controls: From the home screen or Google Now launcher, say "OK Google" and you're prompted to speak voice commands, ranging from making phone calls to sending messages to setting your alarm, among other options. (We highly recommend that you tell Google to make you a sandwich.) This won't be showing up on every Android 4.4 device, so it's only available on the Nexus 5 for now. There's also one other significant problem with it -- you can't activate it when the screen is locked or turned off. Or when you're in the middle of another app. For what it's worth, Google has claimed a huge improvement to its voice-recognition software. Indeed, we had very few problems with the system transcribing our commands.

Hangouts, phone and Email

A few apps received much-needed overhauls with KitKat. The biggest one is arguably Hangouts, which finally integrates SMS and MMS messages into the app. It's great to be able to have all of your conversations finally showing up in one place, but it's still not possible to merge text messages and Hangout conversations together into one thread, so it was too commonplace for us to accidentally send what was intended to be a text message to a Hangout associated with the same person's email address. This is a crucial feature that will likely show up in a future version of Android, but at least Google seems to have full convergence as an end goal. Fortunately, if this isn't quite your thing, or if you're waiting for Hangouts to mature a bit, Google's added the option to change your default messaging app to a third-party service.

Google also revamped the phone app. The dialer is essentially the same, but the main screen also features a list of those people you talk to the most (regardless of who is making the calls and who is receiving them). The phone app also offers new search capabilities that let you look up businesses, contacts and other people within your Google Apps domains. It even includes Caller ID, which shows the name of businesses when they call you.

The standard Email client has also received a facelift -- so much so that if you're not looking closely you might mistake it for the Gmail app. The two now look strikingly similar, right down to the avatar boxes and slide-to-delete gestures. And that's not all: You can now delete or archive an email directly from the notification menu, rather than being forced to go into the app. Overall, this is a huge improvement -- we couldn't stand the user experience in this app prior to KitKat.

NFC

Slip an AT&T SIM in the Nexus 5 and fire up the preloaded Google Wallet app when you get the chance. Surprise -- Wallet actually works. With Android 4.4, Google's ready to go over the heads of carriers that insist on only supporting specific mobile payment partners (AT&T, for instance, is tied to Isis), by simply adding software features that eliminate the need for any carrier involvement.

How is this possible? Google has added something called Host Card Emulation, which allows any app on any device to emulate an NFC smart card, with no carrier-provisioned secure element required (though you can still use them if you prefer). In other words, all of your tap-to-pay transactions can go through whichever service you choose, regardless of which mobile operator you're using. The only thing your phone needs to make this happen is an NFC controller.

Miscellaneous features

Google is also heavily emphasizing document sharing and expanded connectivity options. KitKat marks the debut of QuickOffice as a pre-loaded app (we've seen it show up on other Android devices before, but just not on phones running the stock version of Android). In addition, KitKat ushers in new connectivity features like built-in wireless printing capabilities. The downloads app is also redesigned. We do have to wonder, though, what purpose QuickOffice serves on a platform that already comes with Google Drive, which offers a similar feature set. Perhaps we'll eventually see a convergence between the two apps, but for now this is at least a welcome addition to the list of standard apps.

Screen recording is another new feature made possible through KitKat, but it's not for the everyday user; the phone (in our case, the Nexus 5) needs to be connected to your computer. We won't outline the specific steps here, but we'll link to a post that talks you through the process. What's more, the full clip (which is limited to three minute segments, at least for now) is stored on your phone as an MP4 file until you're ready to share it or transfer it back to your computer. The ability to make videos based on what is being displayed on the screen is a huge win for YouTubers and developers interested in doing a walkthrough of their app or game.

KitKat also includes a technique called sensor batching, which is similar to a few of the features offered by Apple's M7 motion-tracking coprocessor. The idea behind sensor batching is to reduce the amount of power taken up by activities that are constantly using sensor data, such as location tracking, fitness and other apps. One particular use case is step detection and step counting; yes, your Android smartphone can now become a glorified pedometer. This appears to be exclusive to the Nexus 5 for now, since it's conditional upon having the necessary hardware, but Google promises that it's working with chip makers to ensure the feature is offered in more phones going forward.

Finally, Android 4.4 brings other incredibly specific features to your phone, such as Closed Captioning, IR blaster support, two new Bluetooth profiles (HOGP and MAP), a new Location Settings tile in the Quick Settings pull-down menu and a built-in Device Manager.

Camera

Smartphone cameras have evolved quite a bit even in the year since the Nexus 4 came out, and so have our expectations about what makes a good imaging experience. We already felt last year's Nexus camera was mediocre, so how will this year's version hold up against the ever-improving competition? The Nexus 5 comes with a camera that offers the same 8-megapixel resolution as its predecessor, and while we acknowledge that there's much more to imaging quality than raw pixel count, it's still an indicator of the direction LG and Google have taken since the last model came out. In this case, we're not off to a good start.

Fortunately, the Nexus 5 is a little better than it sounds, but it also has its fair share of quirks -- some of which carry over from the last Nexus. For instance, the viewfinder is once again in 16:9 aspect ratio, while the actual image itself is 4:3. Worse things could happen, but it's difficult to properly frame a picture the way you want when it comes out with a lot more vertical space than you'd originally planned. We might be a little more forgiving if the viewfinder were intended to take advantage of the full screen à la KitKat, but the black bar still remains at the very bottom.

The stock camera user interface remains the same as Android 4.3, with the only visible change being the addition of a "+" symbol at the end of the HDR option. Yes, the Nexus 5 camera now comes with a feature called HDR+, which according to Google involves taking burst shots and using special algorithms to put them together into one shot. After comparing images taken in automatic mode with those taken in HDR+, we much prefer the latter and default to it in almost every case. The dynamic range is far too short in normal mode -- most darker areas, such as shade, appear way too dark, while areas with higher exposure are simply blown out more often than not -- and this is where HDR+ really shines. Colors pop out a little more; those darker parts of the photos are easier to see and more detailed; and we can actually make out most highlighted areas. With the new HDR, we're able to see objects through bright windows and even the sky is a more realistic shade of blue. Pro tip: Autumn is an incredible time of year for taking HDR photos.

As you've probably discerned by now, shots taken in regular mode are a little too inconsistent for our tastes. The quality of our sample shots ultimately came down to factors like the direction we were facing and what time of day it was. Whenever the sun was behind us, we generally got great images with a solid amount of detail and accurate color. When it was in front of us -- even if not directly -- the picture typically was washed out and/or completely overexposed. We were also completely robbed of a perfect sunset photo opp, thanks to prevailing lens flare.