"frustrating and unfun"
Look, I like defense games, but this sucks. First off, the pacing is way too slow--both in terms of unlocking new turret types and in terms of the speed that the vehicles move. Waiting for them to get to my defenses was very, very boring. Second: I understand that this kind of game doesn't really lend itself to much of a plot, but no story at all would have been better than this--utter tripe with lots of grammatical errors and crappy graphics. Third: the vehicles that shoot back are a very bad idea. The fun of these games is building up huge defenses and watching them grow, not spending every free second checking on the health. Fourth: if you insist on having vehicles that damage the turrets, for fucksake fix the repair costs--even the stupid gatling guns that you can buy new for 200 costs 220 or so to repair from near-death, and having auto-repair turned on for even a couple of turrets will quickly reduce your cash to zero.