One thing I would change, is don't let Viegraff run past the boss at the end of the level, gets extremely annoying when he is running back and forth and not even hitting the boss.
Truly a well thought out game, hoever there is only two things I would fix; The A.I. So that they don't keep going back and forth over the same spots over and over again. And the ability to place the monsters, traps, chest, etc. wherever you want to, other than that, an excellent game!