Mario Kart doesn't hold a candle to this. SEGA and Sumo Digital have giving us kart racing perfected.
The game at higher difficulties does get challenging, like really challenging, like old school challenging. Be ready for that if you want to make it to endgame.
In multiplayer it's a blast, well worth it if you have a large screen for Big Picture.
There's plenty of racing modes and unlocks, stuff for the casual and stuff for the hardcore. Overall, it's great and you owe it to yourself to play this game.

Don't overlook this game. It's a true gem. What you might want to pass off as a "Mariokart clone" is actually a very fun and polished arcade cartoon racer with just enough tweaks to stay fresh with enough traditional elements to make it very easy to pick up and play.
I can't believe I didn't get this sooner. It's well worth it. Split-screen is very well done for those who miss couch-multiplayer and there's enough subtle depth to the game to make true master something to look forward to.
Get it. Get it now!

A very well balanced tower defense game. One of the best I've seen. Pretty to look at with wonderfully diverse strategies to play around with. This is a tower defense game that gets everything right with plenty of variety to keep things from getting old.