Great Game!
I loved the game, the graphics were very good and the plotline was well designed. Although the hero became too powerful at the end (as said by C3ear), the hero did go on a journey and became more powerful, thus fulfilling the requirements of a Heroic Epic. :)
I think it would not harm the game if you took some of the diologue and condensed it into less (e.g. put two lines of text in the same box). Many players want shorter game times.
As for bugs, I ran into few. I think as the game progresses, you should make the simple units more dangerous, not just add extremely powerful bosses.