ugh...last campain has too much luck involved. I noticed that the number of a certain enemy in a wave is pretty much random. You get unlucky one wave with 4 or more of those double machine gun guys in a row and your doomed because its too hard, even with upgraded auto turrets and a disc launcher. Then you play it once more and that particular wave is easy but its too hard on a different wave. Random selection of the number of particular enemies in a wave and random order of enimes sucks.
the little forest level is under rated. Even when i had a glitch where my second mage that i hired would dish out like 8 times the normal damage, i couldn't beat it. If there was a Very Hard rating, i'd give it that. The final levels are too hard unless you have a super-hero or something.
Theres a bug in the game...i'm playing the medium 25 wave level. The diamond scarab (wave 10) is immune to not just slow, but any damage. Not only am I not hitting anything, but it's taking a looooong time for me to die.... other than this, the game is great.