• Ys VIII: Lacrimosa of Dana
• Ys X: Nordics

They look terrible, but are incredible stories and were optimized for Steam Deck. Ys I & II Chronicles also plays great and are fun, though even the remakes feel older. Other Ys games are also fun.

Age of Mythology Retold I think played well and had good controls despite being an RTS.

Halo Master Chief Collection seems to do pretty decent. I played through Reach and most of the first game at least for the single player and enjoyed it.

American Truck Simulator is surprisingly fun and the studio puts ridiculous effort into optimizing for Steam Deck.

Other fun games I’ve played a lot on Steam Deck:

• Just Cause 2
• Overlord 1, Raising Hell, & 2
• Warhammer Inquisitor Martyr
• Gas Guzzlers Extreme
• Warhammer Space Marine (the original)
• Sniper Ghost Warrior 1 & 2 (1 has not aged well but was still fun)
• Saints Row the Third (the original)
• A good amount of Lego games
• Pinball FX3
• Fortix
• Far Cry 2
• Viking Battle for Asgard (no cloud save, be careful and back up game saves)
• The Saboteur (probably one of the greatest forgotten gems of the PS3/X360 era, I think it required minor tweaking to run on Steam Deck)
• Broforce/Expendabros
• Sir Whoopass
• Hustler
• Dungeons of Sundaria
• Shadows Awakening
• Awesome Pea
• Bears, Vodka, Balalaika!
• Disfigured
• Bayonetta
• Redeemer
• Blasphemous
• Parking Garage Rally