300 hours of gameplay with the only frustration being I have to hit "Steam + X" to manually pop open the text editor from time to time says its possible to even play some decade old games.
Timberborn is a favorite of mine and even with tons going on it's a good experience at 800p. I think the Steamdeck is right around 1050/1050ti performance too and that's better than you'd think at 800p. I'm currently playing Doom 2016 at Ultra and the card can pump 110FPS+ (though I'm limited to 60 on the laptop).
2. While not every game is suitable for the Steam Deck, almost every game that was designed to run well on a gaming console will control well on the steam deck, if it's compatible on a software level.
Also, the input mapping is fantastic. It's a little cumbersome but the touchpads work for mouse input and the additional L/R 4 and 5 buttons on the back help.
Honestly, every game that's not certified that I've tried to play, I have been able to craft a control system that feels very nice. The sheer number of buttons helps.
The games that don't, will show yellow "Playable" rating with a notice that fonts might be small and will need magnification. [2]
99% of the time it's not a problem. When it is a problem you can bind a screen magnifier to a key. I still wouldn't want to play some games on it, games that require extensive typing (duskers is a game about piloting drones through a command line, wouldn't want to play that without a bluetooth keyboard), but for the most part it's fine. Most games, even text heavy ones, have big old fonts and large UI elements.
Put differently: unless the game is purpose built from the start as something that works on a 7 inch screen, I am not sure it would be a good idea to play it on a Steam Deck?