I think an info screen at the beginning showing which things are enemies would be really helpful.. I see cute things like teddy bears with balloons and I think "oh! a bonus!" and it ends up killing me...
Urg.. on hard mode I keep getting stuck in places after I finish a battle, even sometimes in the egg room. It makes me have to redo the whole floor because I can't move.
How do you unselect a tower when you are placing it? I ended up having to wait til I got enough money to buy the tower because it wouldnt let me select any of my existing towers