I have a steamdeck and it's brilliant! The main thing is check the proton website for compatibility as a lot of 'non-verified' deck games play well on it despite not yet being verified. Sleeping Dogs for example (a good recommendation for the person who wanted games in more realistic settings).
I have played everything on mine and it handles even newer AAA releases as long as you are prepared to tweak the settings. And of course the more demanding the game the shorter the batrery lasts. I'm currently playing Pokemon Fire Red on mine, you could even emulate Tear of the Kingdom of it (if you owned a switch and a copy of the game for legal purposes

).