I really like this, it has a nice feel and balance to it. I like the use of the different shades of grey and how you've kept them apart to distinguish the different zones (pit / door and wall / floor).
Nice attempt at 4-Lom and Zuckuss using a lego solution... it would be interseting to get a close-up of Zuckuss as he in particular looks really good. I like Dengar's weapon too.
As a suggestion if you were to keep this diorama or were to develop it further, I would perhaps include the central walkway that Vader walks down, the one that splits the pit area into two.
Maybe if the recent UCS SSD came with something like this as a stand alone diorama instead of the awkward way they tried to fit it in the ship it would have been more interesting.
Anyway, Good job...