Hey Nomad, looks really good! The brown toned down the green a little and brought everything together.
Only thing I'd bring up now is the 'feet' or whatever you call them on the legs of the gun were dug in so when it fired it wouldn't jump back and slam into the guys. You might want to just chip away a little of the groundwork there and shove the ends of the legs into it and then build up a little groundwork behind it.
Just nitpicking though- very nice work! I'm glad I don't have photos of my first diorama- you guys would laugh me right off this forum!