Right now, unfortunately, most of the other commentators are right; it's a bit boring. Perhaps adjust the speed of every new tank, so you aren't hitting the same "sweet spot" on the shield with every shot fired. Or have more than one ring of tanks. Also, sticky shield + energy infuser might need to be nerfed. Reporting the score before you die would be nice, too.
Good, but a few things: more levels; the forcefields don't really make sense; the last level is frustrating to the point of making me not want to play it anymore (poor hit detection on the spikes, mostly).
 "Treasure of Cutlass Reef"){kind=icon}
 "Bloons Tower Defense"){kind=icon}
 "Hover Bot Arena"){kind=icon}
 "Shield Defense"){kind=icon}
 "Amberial"){kind=icon}