Have logged about 70hrs on mine since I got it about 70 days ago. Has been great for playing a lot of stuff in my steam catalog I've not gotten around to or hadn't played in a while, definitely the more casual and indie games in my library.
I find at my desktop I'm more inclined to always play my shooters, etc, not what I'd call more casual games. It's perfectly suited for couch gaming and that has probably been the majority of it's use. Lately I've been playing a city builder that sips power, could probably hit 8hr of gameplay on one charge in that game (TheoTown - SC2k type game ported from mobile).
Likewise, I've run Sim City 4 on it no problem, though the controls and text in that game do make it challenging. Likewise, mods should work in it.
EmuDeck is also a great asset if you've got some roms and shouldn't have problems emulating up through Xbox-PS2-Dreamcast IIRC.
Only gripes is that games sometimes have issues with syncing cloud files between my deck and PC and that's kinda made me back off on playing some games where if it doesn't sync at the start, I don't always want to start a new game for fear of it one day syncing and overwriting a PC save, though that doesn't seem likely or something valve would have overlooked.
Other gripe would be some strange behaviors at time due to it being a linux OS. Has been stable for me lately though