i would reccommend either gears 2 or fable 2, depending on your taste at the moment. if you cant decide between those then get ninja blade, its definately worth at a rental at least (i found it fun, but not too intruiging) but i havent played star ocean or guilty gear, so i cant say too much on those games.
have fun on whatever you choose though!
oh and whats the fallout 3 thing? i really liked that game, are there any major additions to the one youre talking about?