I also really like your Grunt but I think th arms look a bit off. He needs short selves with bare forearms, like Recondo has. At lest that is just my opinion.
I also think that something is off with Grunt... but can't put my finger on it!
What I like on him is we get green highlights everywhere (on arms, belt and chest belt) like all these parts were supposed to be put together. Also, I tried to do like Recondo: Pattern on legs with plain chest... but I think Duke's chest is too well known to be re-use...

I used long sleeves like Duke had long sleeves.
I think the main problem with Grunt... is his ugly face

I will try giving him a visor on his helmet!
Martin