Very nice!
This was actually quite fun. Not the flash game I've ever played, but we certainly don't get very many good Mario platformers. I beaten the game without dying, but was left with 1 HP at the end of the boss fight which got surprisingly tough on the third round. The way Mario takes damage is fidgety and can even keep the player from getting away from danger. I would recommend having Mario blink for a second or two indicating vulnerability from further damage. If I, say, jumped on a spiked goomba, I would keep bouncing off it and lose half my health in just a couple seconds. This can be annoying.
I did still like the sense of challenge. The scarcity of health pickups, and the coin health system. The parts where you have to run to the end due to an impending danger (a boulder, or rising lava) had a suspenseful feel when coupled with the great music choices. And that may be the best part of this game, the music. Nice work on getting all those tracks from the Audio Portal rather than ripping straight from the games. It proves the idea that Newgrounds' content is made by everyone, and not from other projects.
I would have liked to see more variety with the enemies though. The environments proved to be more dangerous than the goombas. Why not add in some more baddies from Mario's universe. Koopas, boos, and any one of the wacky enemies of the Paper Mario games. And since this is supposed to be like Super Mario World as well, how about a few small powerups? Maybe some totally new and original ones?
Overall, this wasn't a waste of effort. With more polish and added content, the next one can be a real hit.