The difficulty of each level can be cranked up from 2.0 standard all the way to 9.0. Yeah, you can adjust the difficulty by decimal points. So you can make the game a hard as you want it to be.
Check out Chuggaaconroy's Lets Play of it to see more. I actually bought it because of the Let's Play.
Also, the multi-player is surprisingly good. And the game has a lot of humor to it.