Well, it resembles a tower defense on how the creeps/waves are coming (on fixed paths). Otherwise you don't place towers but tap on the enemies and launch hits (upgradable "basic shots") from the hero. Tap, tap, tap. You earn bonuses by killing two, three or more enemies with one hit (combos).
With the time you earn special abilities in form of magic skills (limited and upgradeable as well) like fire ball, infected grounds or ice storm (launch with swipe gestures from the icon to the place where you want to have them). There are two heroes with slightly different features to choose from before playing. There is enough real time strategy in it.
So far I had fun with the first of three maps/scenarios "forest" (really pretty graphics and animations on iPad 2) but I struggled two times with the much harder second one "near the walls". So I am not sure if the difficulty is well balanced or maybe I didn't get something. Maybe I should try the other hero…
Anyway: 7 of 25 OF achievements unlocked after 15 minutes or so. Will pick it up again for sure. Thx to devs for the freebie!