Defender's Quest: Valley of the Forgotten

The Defender's Quest logo

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).  

Some parts of the game weren't as ergonomic as I would have liked -- eg, you might find yourself rapidly clicking your lightning spell on enemies that are about to get to you, and when you want to re-allocate your skill points, you'll need to click a bunch.  The story also wasn't much to speak of.  As a tower defense, though, it's reasonable.