Cool game. If I can repair the Black Hawk between waves, I should be able to put some sand bags around it also.
But I think you should take out the EOD suits and just add in ~10 more Inf. per EOD suit instead.
Game is a bit glitchy, just hold one of the arrows and repeatedly tap [X] to jump off the 'air'. Once when I fell, I went threw the ground and did not die, but just fell forever. Like others have said, the controls are not very responsive.
I have not found an Earth Spell. I have all of the achievements, so I going to guess it is VERY rare, or there isn't an Earth Spell. The only spells worth using are the 3 healing spells like others have said though.
Okay game. The racing and fighting would be better if it was a mini-game. I sold 2 Ultimate Bugs (both female) for $15,000 each, and was selling level 4 bugs for $5,000 easy.