I'm gonna make some critics here but that's just because I think you have a noble endeavor, so dont take it the wrong way. Some are just my personal opinion and others are my "professional" opinion:
Uglúk - bilwit made a very unique and detailed skin and that uniqueness got completely lost in your version, the standard armored looks bland compared to his. It's good that you assigned him a more accurate face but bilwit's body is more accurate:Your version resembles the nameless shouting uruk in the beginning of the helm's deep battle.
On a technical note the hand doesn't look painted on at all
Wargs - The original warg eyes look much more accurate:And your version of the eyes are not blending well with the existing skin,
Grey Wargs - I think that's a good idea but would have to be taken further to really work well.
Mumakil - The eye got completely butchered here, doesn't even look like an eye anymore, the paint has a strange black shadow around it that makes it look less like paint and I don't see how the glyph on his shoulder relates to harad, looks more egyptian to me, here is something i did a while ago the glyphs match exactly one of the mumakils of the movies. I don't have anything against toning down the brown on the mumakils but I think you've overdone it and now it looks bland.