LBP is lots of fun, and if you like creating stuff, then I'd suggest that. It's certainly the game with the most content / playability.
Wipeout is not merely
a racer, but one of the best
racers available on any platform. If you've played Blur, then this is what Blur copies. The soundtrack is awesome too.
Dead Nation is indeed a top down shooter, and is meant to be fun, but I'm not convinced it's worth the free download compared to the other games.
No interest at all in Ratchet and Clank?
It's the one I'm downloading after Infamous (I already own LBP and Wipeout