Woohoo more Quake ^_^
I think the modelling parts is well done and the face looks really intimidating.
One a personal note, the Fiend resembeled the idea of a weird dog/bull mutant whereas your Fiend reminds me more of a devil shark (lol imagine that thing being amphibeous with fins, gills and stuff like the Gill Beast from Blood).
For something quakish I think it's almost too realistic. It are details like the original having no visible eyes, abnormal long claw-hands and this evil grinning almost human-like mouth.
The last picture on the right reminds me a bit of a raptor, but that's kinda cool too.
Hey, don't get me wrong I know that modelling/sculping is a shitload of work, I tried too once ^^