moonlightgambler: I'm playing alien shooter now and find it dammed hard to get past the third level, but I won't give up it's Do Or Die
kalirion: I basically always try to avoid spending money unless I get stuck, in which case I usually get the next weapon, or maybe some upgrades.
Well a big red armor and a drone can help quite a bit.
I don't remember which level is the third but I remember a level where, out of luck, I just bought these and simply ran into the beasts until I could get the dynamite and blow up the first batch of alien generators. Then after cleaning the rest of the level was more conventional, or at least less stressful, which was a good thing as both my armor and drone was gone, as well as the majority of my ammo for all weapons. :-)
In this game sometimes you have to know how to run into the enemy as there are unlimited generators. On the other hand, keep a close eye on your health bar, keep moving and dodging, and stay alive!!!