Pretty good
Though... the fight scene seemed a bit... abrupt. I mean, yeah, Bowser's always trying to kidnap Peach and Mario usually ends up fighting him... I dunno, maybe I'm too used to the Mario RPG games where Bowser enters the castle, the toads and Luigi panic and hide as he comes up and then makes his big speech about how he's going to kidnap the princess, and THEN Mario beats the crap out of him. And the hand drawn arrows in the stage select thing weren't too great either, would have been better if you'd used vector arrows... but I'm being too picky, this is a decent flash.