Could use some improvements.
It's not "terrible", not by any means, but if you want to develop a good game out of this there are quite a few improvements that you could, and that I think you should, make to this game.
First of all, you could definitely use sound. For example, since you're using Paper Mario characters, why not the music from Paper Mario as well? Fitting music can add to any submission, and this one as much as any soundless submission I've yet seen.
Next suggestion: more moves. Fireballs, jump kicks, and guns are all good and well, but the addition of more moves (Bob-ombs, Koopa shells, Mario's hammer) would make this a more interesting game by far. And another thing that ties in with that, Bowser should have some moves of his own. Perhaps even make it a full-fledged fight between them, with health bars, counters, and all.
Now for the good things about this game. It's somewhat fun to play (though it is far too short and limited), it's got better graphics than half the movies or games I see on this site, and rather than using verused SNES-style sprites you decided to take the road less traveled and use Paper Mario-type graphics, which is definitely a nice change. But overall it's slightly less than average.
2/5, 4/10.