Long-winded rant ahead (the gist of it is that your image is awesome):
I know this makes me a traitor to my generation, but I like '70s and '80s horror movie special effects better than modern CGI ones. For example, I will always think the 1982 version of "The Thing" looks about 5x better than the [admittedly pretty cool] giant worm at the end of "Hellboy". The main reason for this is the gross, hand-on approach they had to crafting beasties back then, because they couldn't rely on computer graphics -- for example, there were actual pieces of seafood used for the facehugger autopsy scene in the original "Alien". These days it's usually cheaper to render a dripping sewer-monster or flying polyp in, like, 3d Studio Max or something, but I am beset by a sad nostalgia for the days when animatronics and prosthetics walked the Earth.
I'm bringing this up because this image reminds me of the finest hand-crafted slime-demons of days gone by. The details are amazing; it must've taken you hours or even days to get everything just right. That eye -- or more accurately, the *emotion* in that eye -- makes me genuinely uneasy, and the terror expressed in the face as a whole (well, what's left of it) is more effective than any audible scream. It's hard to stop myself from imagining a history behind this picture, like what awful things might've been done to the person to turn them into the end result. The concept of taking humanity and twisting it is especially interesting/scary to me and you've expressed it perfectly here.
I'm sorry that I'm not smart enough to give you a really in-depth critique, but I wanted you to know that I think you did a great job and have really freaked me out. Well done!