Okay this is just my opinion
-1st Signature.
I like the background and that kiinda smoke efect u used but another kind of render may have worked better like a more realistic one.
-2nd Signature.
Love it looks perfect to me <3 onlly those red parts looks out of place if you made all the background of blue tones will look better.
-3rd Signature.
Like the kinda bloody idea but maybe some more iner and outer drop shadow could have made the render blend better with the background imo also adding some of those black lines over the character will make it look more detailed imo.
-4th signature.
Render look pixelated like whne u do a bad resizing and i see some white pixels at some parts.
-5ft Signature.
I like what u did with the render and the efects you added tho kinda dont like the bakground so much maybe because of all those sharp pixels.
Overall good stuff but somethings looks a bit out of place imo.
Wanna see what else you can make.
+1