@ radar816: are you only aiming at the head? Aiming at the body will get a hit almost 100% of the time with a shotgun. Oh, and make sure you're not shooting them from 100m away. Shotguns only have an effective range up to 75m.
This game has the exact same music as the "Don't Steal My Treasures!" or whatever tower defense game. The one where you are the bad guys guarding gems.
I also don't like how you automatically switch to your main weapon when you hit a check point AND how after it said "mission accomplished" and I started typing this thing up, the damn bomb in level 2 exploded anyway. What the hell?