My 2 cents
i think the smoke should be blended out a little more and should continue on around the figure insted of being cut off. some parts of the smoke should be hard edged but should fade off in distance.
this pose is a really hard one to pull off but i thank u have rendered it quite sufficently to get more of a forced perspective or forshortend look u might wana make the head or helmet smaller idk its really up to u.
His Right hand looks a little awakward so if u can find some ref pics it might help better render it.
to finish off u porbably wana clean up some of the lines in the distance and clean up the cicular holes and blend some of the gradiations they look a little stringie right now
o and the red fog around the bottom is a little awakward so maby if theirs a version with out it would help with the critique
Thanks for postiing it i think this will really turn out nicely so just go for it