So it took me a couple of days to fully realize and appreciate the depth of the experience, but now that I've gotten behind it, ModNation Racers is totally incredible. I think many of the reviews have sold it short, between the core gameplay which is a riot, the amount of content already available from United Front Games, and the staggering amount of user-generated content that is out there, this is the total package for racing games, and it's well-worth the ticket price.
This is the game that you play split-screen with 3 friends, and nobody wants to go home at the end of the night. Friends say "I'm buying a PS3, that's it". It's the game in which you can easily join online matches and gain XP to rank up in a competitive environment. It's a game in which you and your friends will easily chew through an hour thinking of Mods to download (EVERYONE is there, from Thundercats, Ninja Turtles, Mario Kart characters, X-Men, Street Fighter characters to obscure movie actors and even dead totalitarian dictators). The challenge is finding a character NOT already uploaded by some sharp mind out there, and you can spend almost as much time looking for content as playing it, without even noticing.
Then we have the creation tools themselves. Incredibly easy to use, but with enough depth to create almost anything you can imagine. Creating and publishing a track is as simple as you could hope. Getting another player to try your map is as easy as driving up to them in the online lobby (MNR's main lobby hub is an online interface full of fellow racers, like Playstation Home, but with cars) and challenging them to a race.
There are enough cars, mods, tracks and modes to keep your racing jones satisfied for quite some time, and when you throw user-created content into the mix, this game goes way above and beyond.
I am going to give this one a full review, so I won't keep hyping it up here, but suffice it to say I love it and think it's just as great and unique as LittleBigPlanet for embodying the Play, Create, Share motto.
If you are on the fence like I was, don't be, this game is awesome. It has been described as Mario Kart meets LittleBigPlanet, and it lives up to both of those names and comparisons.