Yakuza 3: Fantastic story, great characters with solid development, lots of things to do, funny moments like revelations, and fun combat.
Yakuza 4: See Y3
Valkyria Chronicles: Outstanding gameplay, and each battle is pretty much unique; each battle has their own twists.
Ratchet & Clank Future: Fun, charming, funny characters (Quark and Clank mostly), lots of crazy weapons, magnificent graphics, etc. The games are a little easy though.
Folklore: Beautiful soundtrack, great art direction, story full of suspense and mystery, and great usage of the sixaxis feature. The only bad thing about Folklore is that you have to go through the same levels twice.
I don't recommend MGS4. If you haven't played the previous games, don't bother playing it until you've played them.
