I like it! ...for the most part. For a free game on the Internet, it's quite impressive!
Given the name, I expected something more akin to a Mario version of a fighter like Mortal Kombat. This was more like a Mario version of Kung Fu or Ninja Gaiden, especially with the wall-to-wall jumping and blind leaps of faith in the latter case!
I thought that a single attack button would have been limiting and tiresome, but that wasn't the case at all and there was a fair variety with the punches.
If there's ever an updated version of this game in the future, then it should incorporate more henchmen enemies than just red shelled Koopas alone.
Moreover, it needs to be a bit more Mario like. Beyond not having any of the classic power ups, it was strange that I couldn't jump onto the Koopas and kick around their shells!
Finally, Bowser is much too difficult. At a certain point, well before his health meter approaches empty: he erupts with a wall of fireballs that literally spans the entire screen and not only kills Mario but knocks around the next Mario that respawns too! Has anyone ever beaten this Bowser?
Beyond those constructive criticisms, I give this game a hearty thumbs up and look forward to any additional future such games!
I kept aggressively wailing away at Bowser with punches, not letting up or stalling at all, and yet Bowser would still eventually erupt before his health bar would reach the quarter full mark and start spamming the screen with a dense, inescapable torrent of fireballs regardless. I was able to knock him off the bridge several times as well, but that had no real effect.
Granted, I only played this game for the first time last night and gave up on Bowser after only a few minutes of being slaughtered with the aforementioned wall of fireballs.
If Bowser is indeed beatable and had been beaten by several people as you say, then perhaps I was too quick to dismiss him as "much too" difficult and I'll give it another go at another time.
The game is indeed a good start towards the larger game that you describe.