Little Big Mario Kart
Modnation Racers is basically Little Big Mario Kart. Essentially a kart racer with the ability to customize your character, kart and design your own tracks giving PS3 owners a kart racer to call their own.
Now I will say first off if you get this game and your PS3 is not hooked up to the web, you're going to be disappointed by the out of the box offerings. A few generic tracks, cars and four bland avatars is all you start out with so if you don't have your PS3 hooked up to the web, you will probably tired of this really fast.
You can play a career mode which I always thought was dumb to have in a kart racer which most buy to play with others. As I tried to play through the story mode I was reminded why Diddy Kong Racing's adventure mode sucked. Namely it was just tedium of doing races over and over again to unlock everything. While LBP had a Pixar-esque sense of wonder to its story mode, Modnation's story feels like one of the lesser Dreamworks movies, full of stupid pop culture references and trying too hard to be funny. Each race has tokens to collect and objectives to be met along with getting first if you want to unlock more customizable options for yourself.
Controls are decent though the analog steering felt very slippery and anyone who's played Mario Kart is going to have to learn a new control scheme with the right trigger being the gas now. So many times I felt compelled to press X only to remember that wasn't the gas.
Many who curse at Mario Kart will like Modnation Racers as it does have a bit more skill involved. Drifting and doing tricks builds up a power meter that will let you boost at will or bring up a temporary shield to deflect enemy attacks. Speaking of items, MR's items are upgradeable so the more item pods you collect the more powerful your attacks can be.
As user generated content goes, there's plenty to see and do especially in terms of colorful karts and characters. You could created a Mario/Sonic/Futurama/Naruto crossover racer and have them all drive the Mystery Machine and finding the creations you want is pretty well streamlined. However with all this user content comes horribly long load times. User made tracks like LBP's levels are hit or miss. And all too often the top ranked ones are just HD versions of MK tracks which is fine if all you wanted was Mario Kart HD.
But as kart racers go, Modnation will enter the ranks of "not terrible MK clones." Gives itself enough distinction to not feel like a blatant ripoff and for some will feel less cheap when playing the AI but it needs more compelling in game content. Not to mention total lack of a battle mode.