Great game but I had a few problems with it.
First off you had to completely rely on the rats and spiders for everything. The skeletons and ghouls are to expensive to use as a main line. I would suggest cutting down on their bonus effect costs from 75 to like 50.
Aside from that the game was pretty dang buggy when it came to the upgrades for the big mobs. Not the direct upgrades like their abilities and their attack power but the 20 point upgrades for the nests I guess I could say would go to the ghouls and skeletons selection no matter what I did including unlocking them both, and when I did have them both unlocked the big mob's buffer would override the crypts upgrades making it cost 150 for those upgrades.
Another glitch type that I ran into would be that when you get the upgrade for the beast nests level upgrade I mean they would only go up 1 level and after that they would keep eating up resource and never level.
And the final glitch that I noticed was every so often mobs would be attacking my defenders and my defenders would Not attack back but at least this one is correctable later on in the game with fear.
I feel that if you got the glitches out of the game I could give you a 5 =)
Yet again awesome game with those minor complaints aside