I loved Simpsons Hit & Run.
Because by going around, you uncover hidden gags and find collection cards, hidden bees, alien cola machine and alien crates. You could also see how Springfield really is. You could know how far is the elementary school from Bart and Lisa's house and all those goodies. I gotta say, even 9 years I bought the game, I still enjoy going through every map because I keep discovering cool stuffs by strolling around.