MNR doesn't do an awful much for the genre in terms of ingenuity but high production values and a case of "picking the right influences" make Mod Nation Racers an amazing Kart Racing game, probably one of the best ever created.
The thing about this game that struck me the most is the amount of polish it has for being a first entry. I's like they set out to beat all Kart Racing games in every possible way, and managed to pull it off. MNR It has a really really tight gameplay, great graphics, an amazing level creator and community.
MNR level creator and aesthetics own a lot to Little Big Planet, and though they are different games I think It's impossible not to draw some comparisons. I've both games and while LBP was almost perfect there were some flaws here and there, completely forgivable in such an amazing feat of game design but MNR -again-, lacks any similar problems and has an amount of polish that is just mind blowing. One gripe I have, that is entirely technical, is that the loadings stretch a little too long.
Also the level creator is incredibly straightforward and fun to use. Once you get the hang on it you can make anything you want in less than 30 minutes. Even so I find myself spending like 5 hours building a track to perfection.
Overall this is an amazing game, packed of features and with not big flaws so to speak. But flawless doesn't make a cult classic, it's very derivative, albeit in a good way, but fails to break away from if influences.