Summary: Would have rated this as 6 a year ago for incosistent difficulty and need to backtrack, but the developers really polished it since then. Now, in 2013., it's a wonderful game. Great visual style, brilliant soundtrack, plays really quickly, no fussing to get to the point.
Summary: Very interesting game-play, keeps you thinking about not just the approaching enemies but also your resource supply and income (you need this to build). Like what's been said; it's tower defence and RTS combined so it's hard even calling it "tower defence" in the first place.
Summary: Best tower defense game I've played in a long time. Difficult, no broken mechanics, randomly generated hours of fun. Enemies do not follow a fixed path and adapt to the situation. The graphics style has a retro theme and the game is quite challenging.