Tough one actually,
I got a few, but these are my top picks:
-
OG GTA San Andreas (IMHO, the best map and story) has lots of stuff to do, including an online community long before GTA Online was a thing.
-
Sleeping Dogs (quite an underrated game even though it is getting more attention recently).
-
An old-school platformer one: Jazz Jackrabbit 2 (great OST, fun game to play)