I remember playing a game like this before, can't remember what it was called though!
I found it hard to progress beyond a few levels because I ran out of teleports so there was nothing I could do. I seem to remember in the version I played before that you could cause the nasties to collide and create an object equivalent to the land mines that kills other nasties. I'd say you need something else like that which allows the player to continue playing. Unless I'm just not very good at it of course, how many levels could you play through?
I also noticed that one time at the start of a level I appeared underneath one of the nasties. It would be better to check for that when placing the player and pick another spot if it's already occupied.
Cheers,
Dave
http://www.smudgedcat.com