I've been playing Dead Nation with Danielle and have been having a blast - although it's a game we've certainly not found easy, and we're playing on Normal level (there are three more difficulties above this, so... xD). It's definitely fun though, and I imagine has some decent replayability. Still, if you are playing solo, I get the feeling that Infamous might be the better option. I'm not big on sandbox / open-world games which I understand Infamous is, but you never know.
Have played all but Infamous now, actually, which was still installing last night. Quite like Ratchet & Clank, I have to say. Been a while since I came across a game in that style, I think the last time would be Crash Bandicoot. I've got a R&C game on the PSP somewhere too which I've barely got into yet, so it'll be good fun to play that on the bus as well. So many games now, so little time!
Dreamer: I didn't get that problem at all. Are you sure you've only got one of the games? Check your 'purchased' games in the top right of the PS Store. If you only have one of them there, give Sony a call.