You overuse the speed effects, the punches and kicks lack power in them (adding minor tremor during each punch might fix dat), the moves are Stop&Go-ish, but i like the animation as a whole.
The only thing i may recommend you is to read tutorials, especially "Timing, Spacing and Poses" by Foley, it's hella useful (and long):
Click Me and practice a lot.
Good luck with animating and have a nice day.