Looking good so far. I had a hard time cutting off that neck ball joint, but it was definitely worth it! I'm sure he'll look pretty cool with the removable helmet.
I notice that everybody is using those BBi shoulder harness straps, but none of the BBi figures at my TRU have them, is it just my TRU or are those straps from an older figure?
The only thing that I would recommend for your Gree right now is to lighten up the thigh/crotch/forearm color scheme. I'm pretty sure it was a bit lighter than that. Still, he looks excellent so far so that recommendation is just a minor nitpick and he would look fine if you left him.
Are you going to use the "concept" helmet or the "movie" helmet?