Pretty good for what it is and I don't even like tower defense kind of games.
One thing is the cleanse warlocks are entirely useless. Even fully leveled-up, their protection radius is small and you should be putting someone more valuable there, such as another goblin, a healer, a golem, or a turtle.
Best strategy is put a turtle at both ends, sandwich your goblins in the middle, and put a healer near (but on the inside) of both ends as well, and also at least one mana-generator is near-essential. Other than that choose if you want an extra mana-generator, another goblin, a golem, or really anything except the useless cleanse warlock.
So here's the thing. There's only a few stages where the cleanse warlock could even potentially be useful, namely those stages with fog (and maybe the ones with holy towers). But because the radius of protection is so small and you waste a spot a better soldier could have occupied, it's a complete waste. Just deal with the bog towers and holy towers using stuns or earthquakes, exclusively.
What could have saved the cleanse warlocks? Well the cleanse radius should have been the entire field, at the very least when they were fully powered cleanse warlock. This is the only way that unit would have been even slightly useful.