pretty cool
it was worth just getting to lvl 25 just to see my athlon 64 3200 get killed by a flash game lol, was sort of a pity there wasn't much else, having gotten the weapon by lvl 7 and it being very repetitive
perhaps after so many lvls bugs go and in come soldiers with guns completly changing the play dynamic, or perhaps terrain that can black line of fire/enemy movement, also the minigun was too powerful
another thing that has recently come into defender games is support buildings, they are also cool
the reason i also gave the sound a 4 is that the minigun gave me a headache and the bugs made no noise which was wierd, i had my own background music on so i can't comment on yours
but overall very cool, keep up the good work