Defender's Quest is an RPG tower defense. Your "towers" are archers, mages, and warriors, and you can equip them, level up, and allocate skill points.
I got the game through a Humble Bundle, and it was fairly good. The basic game isn't that long, but if you want to 100% it, it'll take a while (you have to play through the whole game and the whole New Game+ with only your six basic towers and without recruiting additional towers, and then you have to level up a whole additional batch to beat some of the extra levels).