Pretty good game but...
The fact that it was pretty much modelled after the old NES and SNES boxing games kind of turned me off. Sure, it's nice to see it appear again, but it's sort of been done before on Newgrounds, and with robots too.
Personally, the game was played pretty well. The fact that there was no apparent, or expected, pattern to the AI's attacks made it interesting to play. Dodging could be a little painful to time, but it isn't impossible, nor very hard. One thing I didn't really get was if ducking or blocking really was very different. It seemed like I didn't really have to duck very often as most attacks could be blocked instead and damage incurred while blocking wasn't too much to handle.
The controls were simple, which is good, but it would have been a lot more interesting if you'd have deviated from the traditional control scheme. For instance, having more than just a right and left attack and adding combos such as up+z/x would cause you to do some sort of special attack at the expense of nearly maxing out your heat bar.
All in all though, you did a pretty decent job.