I played modnation racers and LBP karting, but they both don't have a roster that I'm interested in. Mario kart, Diddy Kong Racing, Sonic and Sega Allstars racing, and crash nitro kart are much better games because they have iconic characters in the game. Not randoms that people make up. Anyways, all people did in Modnation racers was try to make characters that looked like existing characters
Well even so, the gameplay is much too slow for my taste. Basically, I was thinking of a Sonic and Sega Allstars Transformed with Sony characters. The Sonic racing game is great, but that's just my opinion.