You don't necessarily need TONS of fast cuts to make a good action MV, but then you do need to use a lot of internal sync, which you didn't do either. The fight scenes in Avatar have a great inherent beat, since the bending choreography is based a lot on martial arts and is punctuated with lots of punches and sweeps combined with fluid movement. I think what tripped you up was your dedication to using only those two fight scenes from the final few episodes. If you had condensed them, and used only the more fast paced scenes, and manipulated footage to beat sync, then interspersed fights from different parts of the series, you could have ended up with a much faster paced video, with the pivotal final fights as an emotional climax that could have tied the whole video together. Action videos end up condensing fights quite a bit as you have to use bits that work, and trim out bits that don't so using more than two fights would pretty much be a must. I think the giant flame blasts, while cool looking, didn't end up doing much for the video after the first one either, but you used them a lot. In my opinion, this video has some pretty good potential, and I see where you were trying to go in terms of mood, but I think you hobbled yourself conceptually. Also, lose the black flashes at the end.