Good game
A fresh twist on the old "protect your" genre. Looking forward to the next one. A few questions/suggestions though.
1) Do the microwave tanks do damage? If not they should, because at the level at which you can afford them there are far too many enemies for slowing one unit at a time to be effective. Also there is a bug with them that causes them to show the promotion icon to show up repeatedly, even after they are maxed out.
2) I didn't notice any way to sell or re-arange your units. This should be a possibility between levels. (If not to sell them at least destroy and replace them)
3) Later in the game the special powers update far too slowly.
4) the 90k and 100k upgrades are just far to expensive to be really useful. Drop their price by about half, and add a truly ueber 100k upgrade. Maybe repair yard (slowly repairs all units) or microwave tower (slows all planes by 25%) or something like that.