Today I checked out Unstoppable Gorg, yet another tower defense game (there was a bit of a wave of them a while back), but the twist of this one is that you place satellites into orbit instead of on fixed ground spots, and you can rotate the orbits around as the enemy waves attack, to defend particular spots on the fly.  Interesting, but not interesting enough to stick with I think, and it was actually fairly difficult.  I kept getting my ass kicked on Medium, and it almost feels like you have to ‘cheat’ by winning on easy to get research tokens to upgrade your satellites first.  It has a nice retro-50s flying saucer B-movie style to it, though.