Win. I REALLY love how you make straight lines seem angled. Like his hat and all.
I mean, this piece has no AA, no smooth shading, no textures, and it's still awesome! 
I really love the palette!
first some advice:
i think if the clouds were a bit smalller, the pice was bigger instead of being so small it wouldn't feel so squash and compaticted. the great thing about this piece is mario and the clouds they have a great use of colors and its all done in the same perspective. the tunnel would haave looked alot better had you kept to that same perspective instead you tried showing both sides of the tunnel, and while i undertand what you were trying to do it wrecks the peice more then it benefits it.
also the ground i think would have looked better doing the same thing you did with the character and clouds. that way the strands of grass won't look so flat. also changing the top part of the gropund so you can see abit of the underneat of it would make that look better also.
now for some love:
overall i like this piece, and i would fav you but for as much as there is good, there is bad so maybe i'll wait and see if you fix this up or if you make something else...
This is great :D Is the pipe meant to be round still, or hexagonal/octagonal?
That's so sweet. I love the idea, and it came out so smooth and beautiful. Great job.
I think the 'M' could be a pixel thicker, but overall, it's really interesting to look at. Nice palette. I've been seeing so many Marios lately.
Haha, Nice work. I really Loved the clouds, and, of course, Mario.
Congratulations. Favorited ;)
Very nice.