I think I hit the "roof". I got to a few hundred feet in altitude, then my plane flipped direction and began a massive nose dive. Luckily it stalled at about 140m and I managed to get back in control. :P
I enjoyed it, however a couple notes.
Currently, you have a limited selection for your power-ups. While this is definitely not a negative thing, the lack of labeling in-game of these power-ups IS a negative thing. I would firstly start by labeling these power-ups.
The Upgrade menu is awkward, simply because you have to stop what you might be doing to pause the game and upgrade your ship. An easier method would be after every "level", as well as increasing the difficulty, give the player a chance to upgrade their ship then, with an upgrade screen between levels.
The gameplay is very good, and it has the makings of a great game. Keep up the good work!
Very promising start, however a couple of things (mostly already been mentioned by others in these comments). It should have different difficulty settings, more complex upgrades, options to play games with more than one opponent, more room to roam (and faster troops speeds) more control over which troops are doing what (Like a drag-select for units in a certain area and a double click for units of a certain type), and a campaign. VERY good looking game so far, keep up the good work! Can't wait to see the improvements you make for the next version :)
Got President Madagascar badge by doing the very popular strategy being posted around here; but I started in Australia :P Took me around 80 days or so. Very enjoyable game :)
 "Flight"){kind=icon}
 "Marcus : Shooting yard."){kind=icon}
 "Save your wife! Ep 1"){kind=icon}
 "Desktop TD Pro"){kind=icon}
 "1 Will Survive"){kind=icon}
 "Pandemic 2"){kind=icon}