hey
I can see you have put alot of work into this, so I'm sorry to hit you with all my comments... anyhows I sees quite a few things that poke out at me :\
firstly his right arm seems disconnected from the body? and the anatomy looks quite odd to me?
the shading/highlighting of his arm and body looks quite flat? pillow and gradiant shading comes to mind? but i dunno...
his legs look quite stiff also, like he has no knees? how can he walk? hehe...
the way his hands are gripped on the weapon, it seems the weapon should be tilted the oposite way and forwards?
everything seems to be conveniently drawn away/apart from each other, facing out flat with nothing overlapping? this would also destroy alot of depth... reminds me of 3d modelling, when firstly modelling a character flat with open arms and legs, before rigging and posing...
the anatomy of the area above the abs looks odd to me? especially in the portrait...
there seems to be no flow from the neck to the body in the portrait?
AND where is his right arm in the portrait?
what I like is the head in both the portrait and the sprite. I also like like the weapon thingy he has in his right hand and think you should somehow incorporate it into the portrait? I also like the form of his woody/stickly figure left arm of the sprite, although it also seems to lack depth?
his pose is also quite boring... especially for the portait!!!
his woody/stickly figure left arm in his portrait looks very very flat, and judging by the way its pointing, it should look like its poping out and grabbing you? alike
Acke's fighter portrait below... AND I wonder why ther are no intertwinded branches in the portrait? as ther seems to be in the sprite? (hehe, I do think that would be very tough to draw)... anyhows you still are not done sprucing it up, hehe

I seem to think ther was very little design/planning before drawing this fighter? I myself usually draw stick figures and sketches on paper trying to come up with good poses and such, and then when starting on my computer I draw a basic figure of how I think the shadows and lighting would be...
sorry I'm just speaking of what comes to mind... I'm quite uncertain of my comments :\ but maybe others with better knowledge can extend on or confirm my comments?
anyhows goodluck with it!
EDIT:I was just thinking a lil, and something came to me... I was thinking that (especially in the portrait), the line art of the body and neck seems seperate from the color/shading/highlightiung? I think they need to become one/whole? if you can understand what I mean? I think doing this will also improve his joint flow? but I dunno, maybe I'm just crazy? hehe

cya