The Steam deck is a handheld console by Valve itself, and it claims to be different. The deck, unlike other available consoles, is a full-fledged PC that is engineered in a handheld form factor. By default, the deck runs on a custom version of the pre-existing Steam OS, a Debian-8 Linux-based operating system. The final software is supposed to be Arch-based with a KDE desktop environment.
Ever since the announcement, the general reaction to it has been a mixed bag. There are a lot of good things too but a fair share of questions has come up as to why is the Steam Deck even a thing? Valve seemed to announce it out of nowhere and many people were caught off-guard.

Since the deck is essentially a Linux-based gaming PC, you can basically play all games that can already run well on Linux via Proton or a native port. Running games using Proton wasn’t a good experience once due to performance issues and a very small library of games. This is no longer the case as the majority of games now run fine. Linux has come a long way in terms of gaming with more available games to a less wonky experience and improvements to Vulkan and OpenGL. But it still has some way to go before it becomes comparable to Windows as currently no alternative to DirectX exists when most modern AAA games utilize DX12 for things like ray tracing. Proton also needs further improvements since it still does have problems with online games.
The most interesting thing to see in the future is how much of an impact will it make. The success of the Steam Deck might catalyze improvements towards native Linux gaming. We might get to see native Linux ports on many modern games to make them run better on the deck. It might just put Linux gaming on track to someday be neck to neck as gaming on Windows.

The deck runs the PC version of the games you already own in your steam library. This is a major advantage since you can avoid rebuying Skyrim on yet another platform.
The steam deck is certainly no monster given its portable shape and the need to control thermals to comfortable levels while not blowing out the battery in under 30 minutes, but it is no slouch either. Valve chose to put a 7-inch 1280×800 60Hz display on the deck. It does appear to run most games fine including modern games, where 1080p would be stretching it too far.
Some people in social media forums seem to dislike the fact that the deck does not have a higher refresh rate option. It’s a fair opinion but a device like this won’t be running the majority of games beyond 60. In such cases, having a higher refresh rate display is largely unnecessary. It will only increase the cost and battery consumption while seldom being able to take advantage of its full potential. Internally it runs an AMD APU and an 8 CU RDNA 2 GPU. This seems adequate given the 720p resolution. 16 Gigabytes of RAM though is no joke and all versions of the deck have it.

As for real-world performance, a Chinese user with dev kit access sheds some light on the current state of the device and how it runs modern games. You can check more about it here on Tomshardware. (https://www.tomshardware.com/news/steam-deck-benchmarks-60-fps-gaming-experience-reasonable-eye-candy) Keep in mind this doesn’t yet paint a full picture of how the final release version may perform, but it does give us a rough idea.
From what we have seen thus far, the body itself appears to be quite a bit bulkier than comparable devices like the Nintendo Switch.
The deck has three main versions based on the internal storage of 64GB, 256GB, and 512GB with price tags of $399, $529, and $649 respectively. However, the 64GB version doesn’t look too enticing as the storage space is way too low to suffice the installation of modern games. Some modern games like Shadow of War won’t fit even if the whole drive was empty. Also, the 64GB version does not have significantly faster NVMe SSD drives like its older brothers. All of these models do have a MicroSD slot for some extra storage, while MicroSD is not the greatest but at it’s good to have options than nothing at all.

If I have to state my own opinion, the biggest draw of the deck has to be its versatility. The deck is basically a full-fledged PC in a small package. Valve has stated multiple times that you can use any peripherals with it similar to any PC or laptop. You can even dock it and connect it to an external monitor to use it as a SteamOS based PC. You can install basically whatever you want as you normally would.
The initial shipments will begin in December 2021 but due to the overwhelming amount of pre-orders Valve has stated that they will ship out more after Q2 2022. With all said and done, Steam Deck is undeniably one of the most interesting product launches to look forward to in the gaming and tech industry.