I don't like the button layout at all. It says 'or press Next' during the diamond bonus, and there is no 'Next' button. And that giant gold 'Skip Level' button is really annoying to someone with no intention of skipping levels. I'd like a retry button up near the top when I lose a level, instead of having to hunt for it in the corner after a diamond falls off.
This storyline is so ripped from The Wheel of Time. People with the Taint being driven mad and making their way into the Blight to defeat Shadowspawn. That's pretty much exactly how the Borderlands handled their male channelers.
Way too many levels require an ace. This is just stupid game design. All the levels should all be completable without the ace, and then the player who wants an ace can go back and replay it. Things like Level 47 that require an ace are just annoying and frustrating with so much pixel-point trial-and-error involved.