First thing i noticed was it was a bit small haha and i agree get rid of the border, maybe add some darker parts near the edges to add depth, the lighting is very strong at the top of the renders head, i can't decide if its too strong or not :/ but i do like the smudging or displacement maps? which ever it is, looks good, maybe change the colour green is his eye to a different one? but again another 50/50 decision i would have to make as Spawn's eye is naturally green and thats who the character is... just pick what parts of this comment you liked and maybe go with some of the ideas other than that it looks great kiu! but definitely get rid of the border

-Dan