The regular game is fine but the challange mode is terrible. It should have been left out. I can't even list everything wrong with it. Just take my word.
This is a cool game, but it gets boring after a while. I also wish there was a save button. And about Viridian's comment, I don't have any clerks and I'm on medium. Rogues and rangers and great. Everyone should have a mage. For the forth spot I chose a knight for a strong attack.