Overall a good game with some issues
I liked this game, the whole 3D-rotate thing resulted in a classical defense game with a twist. The only problems I see are in term of controls.
1) "Z" is not an optimal key to use, as it is in the middle of the keyboard for european layouts. Wasn't that bad as I rarely zoomed in or out anyway.
2) The " ! " on top of the UFOs is unhandy as it blocks the colours from certain directions. It doesn't really make the UFO more visible anyway. I'd delete that, if possible.
3) Some of the sight seeings are so big that you can't target very low missiles anymore, as only the repair button pops up. Might be a feature, but rather looks like a glitch.
Besides that: Cool game.