Just started playing GTA IV on the Steam Deck after having it sitting in my Steam library for years. It's really fun. I really like the protagonist, the setting, and it's openness. It's a bit more tame than GTA V which I have played as well and I prefer the more subdued tone.
Personally, my least favourite gta. Liked the writing and the characters, but for me, it just didn't feel fun to play. A good example of this being the driving. Sure, it was more realistic, but it wasn't enjoyable