Good game, a little easy
This was an excellent game with some nice strategy, like trying for combos, aiming at the right enemies, aiming and timing your shots right. One thing I liked to do was shoot at flying objects so they crash and destroy ground objects--that was a nice touch.
Now, I've only played until level 33, but it all seems a tad easy to me. It may just be that my comp is laggy when a lot's going on, but for the past 10 levels I've been losing only about 50 life per level out of 300-500 life total. Even the level 30 boss only took me down by about 150 out of 300. (also I'd been saving cash to get the 3 missile when the 500,000+ bonus from the boss made that moot, so if I had been getting more upgrades the boss would have been even easier).
Also, maybe you have more kinds of enemies when the level gets higher, but come on--four guys just ain't enough. Helicopter, plane, tank, footman, plus giant wasp--it's too repetitive.
But overall excellent game