First, those are some neat fighter sprites there, they seem to fulfill their purpose.
Now for suggestions to liven things up a little, why dont you change subject matter and frame of reference?
All you've posted here is fighter characters in various fight game styles.
Pixelart is a subset of graphic art and nothing is really set, you've made the common practices of fightgame sprites your frame of reference for pixelart, and burly guys your sole subject matter.
Check most of the top pixelart on Pixeljoint, nobody could tell you what style it is...apart maybe from the style of the guy who did it.
From my point of view just fighter stuff would seem pretty constricting, but maybe it's not like that at all from your point of view, so just my 2cents
I would try to translate some style that I like that isnt pixelart into pixelart...it usually isnt succesful but boy do I ever get obsessed about pics where I do that :p atleast it'd give me some enthusiasm.
Also, have you tried animation? it's always struck me as really weird when people do sprites but only one frame per character...maybe that's what you're missing.