If I remember right the hub in Psychonauts is the summer camp. There you can collect respawning items, talk to characters, and enter the levels (throwing a door on the back of the head of a character).
I never replayed the game and I think it speaks volumes about the originality when I can remember almost every level. The crazy gravity defiant milk man world ("I am the milkman, my milk is delicious"). The artsy spanish/picaso/bullfighting world with playing cards. The fish world where you are a giant monster attacking little fishy towns.
FarCry 2 I had more fun collecting the diamonds than doing anything else. I'm a sucker for hidden items, even if they are marked on radar.
I thought there was some sort of a "zip" in Monkey Island 2?