I have alot of experience with it, having the game on the 360 with everything accomplished, and I'm halfway through the PC version.
It is a tower defense game, but you can control vehicles while you play also, including tanks and planes. There is alot of strategy involved, where you might want to wait til the last possible second to put up a tower, while using a bomber to kill enemy towers, or try to accomplish objectives like challenges while playing.
The art style, sound, graphics and the whole package has the quality of a Blizzard or Sid Meier title; I wouldnt' have bought it again on Steam if it wasn't one of those great games I will play again and again over the years.
But... this is nerfed version. There is no multiplayer, and while you could easily put in 50 hours trying to get General and all challenges done in single player, multiplayer was a blast on the 360 (minus the griefing 'run your planes into the enemy toy box' strat). You can't rebind any keys, so if you like to setup your keys, you need a profile-capable keyboard.
A definate buy, even without the multiplayer and PC perks you might expect. Fun, interesing, and challenging.