Alright.
The first campaign was pretty fun. A nice difficulty gradient, but nothing you couldn't handle if you made the right choices. The graphics were fun, and I enjoyed the upgrade system.
The second campain sucked balls. First off, It would have been better to keep the guns that you just spent the entirety of the first campaign building up. Instead you act like the first campaign never happened. second were the wall enemies, which served as a game killer for me. When you make and enemy that serves as a wall, does it make logical sense that the enemies should be able to shoot bullets the size of your turrets, while you can't squeeze through a pixel-sized machinegun bullet? No, no it doesn't.
Also, a good deal of the guns seemed downright useless, like the droid tower and the mobile airships. I actually died in a level, with all three of my droids still intact, even though they should have been taking the hits. I never even ended up getting the money to check out the higher level guns, which would have been level one and useless anyways, and the fact that you increased the difficulty for the second campaign while RESETTING ALL OF OUR WEAPONS is really a dick move. Try and balance out your games a little more.