No offense to you Selka, but your suggestions are just dripping with personal bias.
Anyway...
RPG:
-FFX and FFXII were excellent; if you've ever played an FF game, liked it, yet are not fanboyishly attached to its traditions (i.e. are somewhat open-minded), I think you will find a lot in them. XII is a big leap in terms of gameplay and mature, nearly cliche-free storytelling, if you're interested. People often complain just because it's not as insanely emotional, the way I see it.
-Kingdom Hearts and its sequel were fun; they had obvious flaws and were nothing very provocative, but they were both very entertaining throughout. The Disney-ridden yet intricate story, along with great music, was, to me, very inspiring.
ADVENTURE:
-Okami's gameplay is much like Zelda's, but its aesthetics and its EXACT mechanics make it a very different experience. Highly recommended.
-Shadow of the Colossus doesn't deserve a placement in genre. It could just as easily be RPG, action, or puzzle. This is epic game poetry, and its also fun. There is much to appreciate in the game, and playing it through will definitely make you FEEL something. The game constantly has your attention, even though it plays off of so few mechanics... OVERT mechanics, that is...
PLATFORMER:
-Ratchet and Clank is wonderful. Deadlocked has more of an arena-style structure with less adventuring, but the first three are a great mix of role-playing, andventure, shooting, and platforming genres.
-The Jak series comes sort of close behind Ratchet. Gameplay is a little stiff in comparison, but the storytelling nearly makes up for it.
ACTION:
-Timesplitters is great multiplayer, with an entertaining single player. A fairly unique-in-style, worthwhile play.
-Splinter Cell has not been mentioned here, has it? Terrible. This is stealth gaming at its finest. Unilke MGS's great action-oriented gameplay and top-tier storytelling (don't get me wrong; if I'd have played any of them yet I'm 100% sure I'd list them here, as I know they are great games), these games make you think your way through missions. First is great, second steps down in general quality, third (I've heard) is the best so far.
-Bully is pure fun with a bit of a social message. Doing the things that are possible in the game are just a blast, and the gameplay is varied throughout. If you liked GTA, it's for you. If you haven't played GTA, don't miss this one.
Games I hear are good:
-Psychonauts
-God of War
-Indigo Prophecy
-Disgaea
EDIT: Added Bully.