i had alot of fun with this game, tips for players are
1) look at the pattern, try to use the same pattern the enemy does, and when you are close to each other, hold space to slow time and shift to shield and get head shots for double damage
2) go back and collect money from easier enemy
3) dont always just buyanything save your money up for something good :D
to the last 3 comments posted, sorry if it sucks, but its my first game all i knew how to do was create a button and use the stop and play action script.