Great memories
Well, I guess it is pretty obvious that you ripped the concept for this game off the old dungeon keeper series... but it's still an entertaining game, even today.
On the plus side, it was good to see that game come back in a small flash game. Like I said, good concept, even years after it was made. Second, UI was generally easy to understand and use. Third, it was not evilly difficult. This is supposed to be an entertaining game of torture and defense, and you got the balancing down quite well.
On the down side, the UI was incredibly bad when an actual battle was going on. I know overlapping sprites are almost inevitable in this type of game, but perhaps an option to see a list of all of the characters on a particular tile would help. Some other thoughts in that same vein might be nice... Second, the music was, well, *snozzzzzzzz*... sleepy. No battle sounds? No victory sounds? Ah well. Third, it could have used a little bit more explaining at parts. I know there were tooltips everywhere, but seeing 8 different stats for each creature can be a little overwhelming when you're actually trying to make base defenses. This could be especially helpful when trying to figure out what element a creature is, for example. Was there elements? I'm not entirely sure at times.
Anyway, this was a nice nostalgic breeze that was pretty well implemented. Nice job.