The courses are great. My favorite is Mushroom City. But they're all well made and fun to play on.
The characters are, well, every Mario character with just a few new racers like (*NOTE* SPOILERS!!!!!!) Toad, Toadette, King Boo, and Petey Pirahna.
The difficulty grows with which cc your playing like 50cc is easy (easier than Mario Kart Wii's!), 100cc is normal, and 150cc is hard. At least the difficulty is a lot more fair than Mario Kart Wii's difficulty!
I'm not going to say that much on graphics because there really isn't much to say about them.
So yeah. I'd get this game. Not rent it, buy it. You'd probably be able to only get it used at Gamestop or EB Games or whichever game store that has used games. It won't be a waste because it's very fun.