Yeah, its a very good game but I can see a few easy to fix things:
Masks: read some tutorials on masks, I will probably post some later, but you should use one for your main character (a drill type thing, wasnt it?)
Collisions: When your character hit the wall you could keep holding the button and keep going in the direction you were hit, just say "collision with wall, move in direction (middle square) speed: 0".
Enemy AI: just work on it a bit, use some paths.