Gaming Board Guru's - Sony Free Content

Little Big Planet is the best value of any game they're offering. It's a platform game that you can create your own levels if you're feeling creative. Or you could play the shite-tons of user created levels that other people made.

InFamous is a solid game but it gets pretty repetitive. It's a sandbox game similar to GTA or Assassins Creed in the sence that you accept missions and complete them how you want to. But like I said, it get to where you feel like you're doing the same missions over and over. Plus, the building climbing gets old quick.
On the plus side though, it has a pretty good story and the artwork and styling is pretty cool imo.

Stardust HD is a fun shooter, but its a PSN game so there isn't a whole lot to it. You play through it once and you're done. It only takes about an hour to beat it on the hardest setting.

Wipeout HD is a PSN racing game. I never played it, but my friend downloaded it a while back and then deleted it a half hour later. Fwiw.

I have no idea what Dead Nation is so I can't help with that.

Being that you've never played any of them, I'd suggest you get LBP and Infamous. They are your best value.

I don't know. I still haven't been given the option to download them.