Vanillaware games runs perfect on Deck.
13 sentinels via yuzu (greatly localized, ryujinx does not get localized languages but yuzu does).
Wii's Muramasa with dolphin+HD texture pack runs perfect
PS3 Odin Sphere Leifthrasir runs perfect
PS3 Dragon's Crown runs perfect
I tried some nukiges and one of the work great with steam proton up.
But the other one didn't have audio on movies using steam compatibility so tried with lutris launcher and added a steam shortcut then movies had audio too.
At this point, one the few games I miss cause I'm not able to make it run the original steam/uplay version or even the pirate versión (tried both) is Tetris Unlimited, I think has something to do with administration permissions but I'm not sure. On windows versión the game makes you to give launcher app administrative privileges repeatedly,
Oh also tried PS3's Marvel Vs. Capcom 2 and Street Fighter 3 Online Edition (imho best SF3 version)
Both run perfect too. This machine is great for fighting games. I was scared for d-pad position but it surprised me.