Okey I just restarted it and I think that I just got lost on my first run, that's why I couldnt find any alien. Now I found a huge amount of them!! Forget the last thing I said, the game is perfect!! :D
Oh jea i definetly need a better idea for spawning enemies in the future. :D But as long as it served a little surprise on your second try it has some sort of purpose.