Tomb Raider Legend. Way too easy and has too much oh-god-don't-get-confused-dear-newbie hand-holding, but getting those hidden rewards is pretty satisfying. Croft Manor is the best level so far (as of Ghana).
Also, Psychonauts. Seems nice so far. Good writing! Not a survival horror clone like Grim Fandango!
Also, WTF (PSP).