My issue with these sprites, and it's a problem I kind of had with Volgarr, too, is that they look kind of muddy. You use too many mid-tones in between other shades of light and dark.
Comparing Ryu to your sprite, Ryu uses 25 colors and your character uses 35 colors.
Look at the arms here. The musculature in Ryu's biceps are clear and defined. You use more colors, more shading, but you lose some of that high contrast easy readability.
Simplicity is your friend. Less colors, more contrast. Brighter brights, darker darks.
Another place to compare is the red on Ken's pants vs. the red on your character's scarf. Ken uses a lot of very bright shades of red with a dark outline to imply shadows around the edge of his legs. It makes him "pop" more. You go for much darker shades of red much more quickly, and it makes things look kind of murky.
More colors like that also mean you're just making more work for yourself. Not only would pulling back a bit maybe look a little better, but it would also be faster in the long run.
That being said, I'm not exactly a great
sprite artist, so I could just be talking out of my ass. And it's worth mentioning that I do think the sprite looks really good (I like the design), and I thought Volgarr looked pretty good, too.
It's just the brightness/contrast/color count thing is a pet peeve of mine, and I've seen a lot of sprite artists fall in to that trap. Hopefully I'm not stepping on any toes in my suggestions.