This is incredibly well done. I see you used the original art too! It's so neat to see someone else's flair used on an existing work. I think you did a great job, and it totally reminds me of those old beat em ups.
The only thing I would suggest is that most pixel shading is done almost in gradients; On his pants and jacket there are just spaces of pure colour with no blending. If you coloured them like you did the chest, it would look even better.