The problem is that the guys run through each other. All you need to do is get a couple guys at their base and you'll take it down easy. The enemy doesn't bother to stop and kill you before moving on.
Yeah quite fun, but quite easy. Only one loss and that was on the challenge where you start with one life. I also agree with below that Ward of Light costs too little.
beat day 40 on norm. The only useful weapons are shotgun and satellite laser. I used shotgun for a long time. For towers get flamer joe as quickly as possible. I got laser turret and missile turret. Eventually I sold joe for a second missile turret. By the end I had fully upgraded towers and satellite laser, ~75 gunmen, and ~70 repairment
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