Amazingly good
What stroked me the most is the polished gameplay, the music and sound effects, animations.
What could be improved in my opinion:
-Graphics, they are about as simple as it could be. I understand it's work-intensive, and the art style/simple animations fits very well in most of the game, but maybe adding some details on the static settings like the title screen and world map could improve it.
-On the engine side, in the barbarian stronghold, when too much enemies remains on the floor, the game speed becomes slow, even on decent computer (core2 2,4 ghz). Probably using a sprite limit on remains should fix this easy. Potentially it could make the overall game faster on slower computer too. Btw, maybe add a note that you can actually play the barbarian stronghold.. ! : ) (or maybe I missed it?)
-Couple other bugs like trowing disappearance but it's not that bad, really.
-Difficulty level is pretty high, having two difficulty setting would be even better. Yes, I have finished the game and got about 150 kills in stronghold.. played alot!
If I were you guys, I would think of going commercial with this game (Xbox live, PSN, etc) with upgraded graphics and some tune up here and there.. ^_^
Very nice job, I had (and a couple friends too) way more fun with this game than castle crashers demo! Best flash game I have ever played!