Pretty decent
The general idea was alright, more original than having him fight some other faceless stick man like many others do. I liked how the weapons were formed and that jump-smash with the pole was pretty great.
There are three main things I feel could be improved.
1. The speed... A lot of it was too slow to feel the intensity of the attacks.
2. The character had noodle arms that would simply curve around... While it's possible for you to develop that into a recognizable style of your own, I felt it took away from the intensity. Having a sharp angle at the elbow when preparing a punch would look a lot more fierce than simply curving your arm to hit the thing in front of you.
3. The lack of background was kinda bland. You could let the character interact with the background (like picking objects up) or smash through one background into another, etc. Having a plain white background is just kinda boring. Even a simple black background with small white dots ("stars") or a typical black background with green grid would be more appealing.
Sound can be synced in flash by going to the properties panel, clicking the frame the song starts on, and selecting "Stream" as the sync option (it's usually on "Event" by default). This will make the music pause when the movie pauses and stuff.