Perfection.
I tried playing the game on here at first, but it was horribly laggy. So I hopped on over to Kongregate, and it worked fine. Nothing impressive with the graphics here, but for a flash game with this much going on, that's probably a good thing. Nice background music too, suits the game quite well. As for the gameplay itself, I don't think I've even seen a Warcraft 3 tower defense with the kind of perfect combination of upgradeable towers and character leveling as I see in this game. Absolutely outstanding. The difficulty scaling was spot on, just about forcing players to play through the Easy maps to gain the flexibility to move on to Medium and Hard, though all one has to do is turn off all of those specializations to get a bigger challenge from the tougher maps. I'd say more, but really I'd just be praising endlessly. An outstanding tower defense, finely tuned and well-executed, if my nine-and-a-half straight hours of gameplay doesn't say that enough. A great deal of kudos to you.