LittleBigPlanet. This was called the saviour of the PS3. Sony marketed the game into high heaven, and made some serious hype. First, lets put this get this out of the way; this isn't Fable, Daikatana, or Spore. Meaning, it delivered.

Basically, the game revolves around it's phrase. Play. Create. Share.
Somewhat self-explanatory, users are allowed to make their own levels and allow other people to play with them in a up to 4 player co-op. Local and Online. You are allowed a huge arsenal of tools and materials to build with. What's amazing though is that the devs gave you the tools they used to make a level, which allows for some interesting levels.

Now, there are quite a few ways that a dev could have seriously screwed this game up, but they didn't. The gameplay is AMAZING. Running through a level working together and at the same time competing with 3 other people is a feeling like no other. The cooperation is phenomenal. For example, the R1 button allows you to grap on to an object or another Sacboy/girl. Suppose you're having trouble getting up a ledge. The other people in the group can actually make a rope of people to get you up the thing. Graphics wise, it looks AMAZING

Now, this is all amazing, but there are flaws. There are some things you simply can't build, such as a timed switch, or a resetting switch. They may not seem like alot, but they're vital to a game like this, which is a serious con. Another one is that the Z dimension is very unresponsive. When in the middle of a jump where it requires you to switch between back and foreground, it may not do this fast enough. And I also heard that moderators are allowed to erase your level without a warning. Bleh.