Jesus, you guys.
I don't know what you guys leaving all the frustrated reviews mean by "trick level". Do you mean level 4? Because the title of that level is the secret to winning that level. It's not that obscure.
I just beat this. It was a lot of fun. I really like how it played. I spentthe first few levels wondering just how the hell this game worked, but once I figured it out I couldn't stop playing.
I played this in multiple sittings, but I still can't help but say that this game was too short.
Maybe different types of enemies and whatnot would be able to add more depth to the game? While this is the best game to implement the idea of evolution in the core gameplay (in my opinion), it still needs something to make it really great. I would try to mess with the formula you've got going here as little as possible, but definitely try to add something more too it.
I hope there's a sequel. I look forward to more games from you.