Closing in on 50 million units sold, it's safe to say Sony's PlayStation 4 has been a huge success, significantly outpacing its closest competition, Microsoft's Xbox One.

But just three years since its debut, Sony has released a hardware step-up model of the PS4, aptly called the PlayStation 4 Pro. As you can guess by the name, this isn't the PlayStation 5. It's fully compatible with all of the existing games, apps and nearly all the PS4 accessories currently on the market (or in your personal collection). The new model hit stores on November 10 for $399 in the US, £349 in the UK and AU$559 in Australia.

Read: Best gaming chairs we've sat in for 2019

But the PS4 Pro promises to deliver better, smoother graphics than its predecessor. You'll only get that graphical upgrade on games with a free downloadable software patch installed. The most noticeable improvements will also likely require TVs with support for 4K resolutions and HDR, the high contrast mode that can offer bright whites and more gradated blacks.

Sarah Tew/CNET

For console gamers who have always looked with envy upon a $3,000-plus PC gaming rig with daisy-chained video cards running games at super-high resolutions, it's certainly a compelling upsell. But -- spoiler alert -- the PS4 Pro didn't leave my jaw dropped. In fact, I often struggled to see any discernible difference between the same games on a Pro and a regular PS4 when played side by side on nearly identical 4K TVs. Out of the gate there only a limited number of titles that are noticeably improved.

So what, exactly, does that mean in terms of a buying recommendation? The short answer is this:

If you already have a PlayStation 4, there's little reason -- so far -- to upgrade to the Pro. But...

If you're buying a PlayStation 4 for the first time, the Pro is a solid investment, if only for its larger 1TB hard drive and some promising new Pro-enhanced games coming in 2017 and beyond. But...

If you're looking to take the PS4 plunge for the first time and you don't have a 4K/HDR TV now -- and have no plans to buy one in the near future -- save some money and get the PS4 Slim, which also includes at least one game.

There are plenty of PS4 holiday shopping deals for the Slim and the Pro, making this the best time to buy either model. The same goes for the Xbox One S, which now competes with the PS4 better than ever before. (Check out related Xbox One holiday shopping deals.)

Update, November 21, 2016: Added more impressions of PS4 Pro games and ratings, and acknowledgment that some games have been found to run worse in their enhanced Pro versions.

Sarah Tew/CNET

What's new and different about the PS4 Pro

The PlayStation 4 Pro is essentially a PS4 with better hardware inside that's designed to improve the performance and visuals beyond what's currently possible on a standard PS4. Not every PS4 game can take advantage of the Pro, but it will play any PS4 game you throw at it.

A regular PS4 game will need a downloadable patch to support the PS4 Pro's upgrades, but it's still unclear what exactly each patch will provide. For any given title, a Pro update will bring some or all of the following enhancements: better frame rates, higher output resolution, better textures and HDR support. That latter feature, however, is also available on the non-Pro PS4 consoles following a September software update. Judging from the updates we've seen so far, there doesn't seem to be any rhyme or reason in regard to which games get what.

Only a small number of games with Pro patches were live for us before review time, but Sony promises that 30-plus games will have Pro patches at launch, totaling 45 by the end of 2016. Starting next year with games such as Horizon Zero Dawn, Days Gone and Mass Effect Andromeda, you'll start to see a "PS4 Pro Enhanced" badge on the box art of games that have Pro support already built in. Sony says that almost every game released on PS4 from here on out can have Pro perks.

Enlarge Image Sony

Physically, the PS4 Pro looks like a beefier PS4 Slim. Its footprint is a bit larger but it's not much bulkier than the original 2013 PS4. It casts a thin, horizontal LED light (blue, orange and white) from the front of the unit when in different modes of operation.

Thankfully, the Pro brings back the optical audio port that the Slim omitted while adding an extra USB port around back. Like the Slim, the Pro also supports the fastest Wi-Fi protocols (802.11ac), and it also has dual-band support (it can use both a 2.4GHz or 5GHz signal).

Sony has confirmed that the console makes use of the SATA-III specification too, which theoretically means you could install a solid-state drive to take advantage of quicker read times. (Although all PS4s support user-upgradeable storage with standard 2.5-inch drives.)

We're testing that out separately and will report on what we find. Either way, it's good to know anyone can still swap out the stock drive for a new one.

Sarah Tew/CNET

Other exclusive features

The PS4 Pro will launch with Netflix support at 4K resolution in addition to a YouTube app with 4K and HDR compatibility. More apps will open up support for 4K and HDR features as the platform matures.

Also exclusive to the PS4 Pro is improved bandwidth for the Remote Play and Share Play options, which let you stream gameplay over the internet. Both modes will be able to share, stream and play at 1080p, which is a bump up from the standard PS4's 720p cap.

Of course I need to bring up the most glaring of missing features: 4K Ultra HD Blu-ray playback. For whatever reason, the PS4 Pro cannot play these discs (unlike the Xbox One S ( )). Standard Blu-rays will be upscaled to fit 4K screens, however.

The technical gap

One of the big frustrations of my initial experience with PS4 Pro-compatible games was trying to manage my expectations. That's because Sony's labelling of which games support which video upgrade is vague at best.

By looking at a title's version history from the PS4 menu, you can get a tiny bit of insight as to what's been added. For instance, The Last of Us: Remastered says the latest version offers "PS4 Pro Support," but Shadow of Mordor simply states "4K Support."

There's an inconsistency here that's tough to follow, not to mention I don't know if 4K really means what you might think it means. On Sony's PS4 Pro site, a disclaimer reads that the console offers "dynamic 4K" which means, as it explains with a footnote, "Dynamic 4K gaming outputted by graphic rendering or upscaled to 4K resolution."

I'm not sure that means native 4K (3,840x2,160-pixel resolution), which is four times what you can get from a "standard" HDTV's 1,920x1080 resolution. Considering that PCs with much more impressive hardware than the PS4 Pro can struggle to even reach native 4K at 30 frames per second (the absolute minimum required for smooth gameplay or video), it may seem hard to believe the PS4 Pro can output such a technically demanding video signal without some serious compromises. Well, it doesn't.

Indeed, the Pro uses some common tricks of the trade, including anti-aliasing, checkerboard rendering and geometry rendering. Effectively, that means that the games have horizontal resolutions such as 1728p, 1800p or 1952p. Then the games upscale to 2160p as needed, all the while balancing graphical sharpness with the all-important frame rate. (Indeed, this same upscaling technique is also widely used in the last generation of game consoles, too.)