Been loving mine these past few months. I've mostly used it for emulation and PC games from the 2000s, nothing too demanding.
N64; Goldeneye 007, Mario Golf, Mario Kart, Perfect Dark, Super Smash Bros
PS2; Ace Combat 4, Killzone, SSX Tricky, Tony Hawk Pro Skater 3 & 4
Gamecube; Luigi's Mansion, Mario Kart DD, Pikmin 1 & 2, Super Mario Sunshine
PC: Brutal Legend, Bully, Commander Keen 4, Crazy Taxi 3, Duke Nukem Forever, Left 4 Dead 2, Portal 1 & 2, Postal 2, Prince of Persia SOT, Pure (2008), Simpsons H&R, Space Cadet Pinball, Turok 1 & 2 (2015 remaster), Wolfenstein (2009)
The only real "modern" titles I've played are Doom (2016) and the Spyro Reignited Trilogy. Both play fantastic.
Overall the system is 95% perfect. It has it's hiccups and some games you really have to tinker with to get playing nicely, but it's exceeded my expectations by far. I feel like I'm 7 or 8 years-old again with my copy of Link's Awakening on GameBoy! Best $500 I've spent in years.
Sad to say, but I've more-or-less completely abandoned my PS Vita and Pandora 1Ghz.
EDIT: forgot to mention, there have been a few games I haven't been able to get working properly (eg. Soldier of Fortune, runs but has texture issues).
EDIT2: Finally got SOF working nicely!
- install CD copy of SOF Platinum on PC (GOG version probably works but make sure you use correct SOFplus patch)
- install SOFplus fan patch
- modify config to 16:10 aspect ratio (see SOFplus notes about FOV cvar)
- copy installation folder to Deck
- add as non-steam game using Proton GE compatibility
- set video driver to QeffectsGL
I was meaning "Download while the Deck is in Standybe Mode
Standby on the Steam Deck is the same as a desktop/laptop PC in sleep mode with a halted CPU, so downloading/updating isn't possible.