Time for me, the eternal lurker, to contribute.
+1 EXIT 2
Game with no killing, is it good? Yes it is! Puzzle-based action as an escape artist.
+1 God of War: Chais of Olympus
Since God of War is awesome, this must be too. Maybe too short but still excellent.
+1 Patapon
Really innovative gameplay and weird battle system, in a good way.
+1 Pursuit Force
I never cared for driving games but this hit the spot because it mixes action, stunts and ... something. Only downside is those lame shooting scenes.
+1 Ratchet & Clank: Size Matters
I wouldn't have believed but this is actually a good action-platformer.
+1 Star Ocean: First Departure
Oh god this is addictive, one of the best PSP RPGs.
-1 Final Fantasy Tactics: The War of the Lions
In my opinion, they ruined completely good game with hastily coding and trying to add new 'cool' classes. I just can't stand lagging when casting spells or even when critical hitting. Just plain crap I say, original is much better. Only good addition is those neato CGI-movies.
EDIT: Forgot to arrange alphabetically and fixed some typos.