Fun game overall, but as mentioned earlier (and just like in the first game) there's no way to improve after being defeated in a level - not even redistribute funds and change upgrades, leaving as the only options trying again and again and again... or starting from scratch.
Graphics were nice, not great.
I've a feeling that placing anti-air towers at the bottom of the screen is useless since enemies hardly ever enter their range that way, not sure... In general the air defenses were definitely too weak, ground enemies take time to fight the towers and run into mines, air enemies just fly in and bombard the main tower :(
The action is quite chaotic, I think I'd prefer a stronger main gun (it runs out of power rather quickly) since the turrets are easily destroyed without me noticing and it takes time to rebuild.