Posty1978,
Is this 1:72 scale? First let me say the construction and painting of the vehicle and figures look to be pretty nice. A closer photo of either of these would be nice. They appear to have a glossy sheen but that may be the photography. Secondly, the groundwork looks pretty good although there probably could be more foliage. I like the water effect also.
Now for the constructive criticism part:
The layout needs work. One of the classic 'rules' of dioramas is not to run items such as the wall and tank parallel to the sides of the diorama base. Running these things at angles would make viewing the dio more interesting and less regimented.
The base. You should probably put more thought into what the base is made out of rather than using a cardboard box. I don't imagine the box would last very long if you were carting the diorama from show to show. The finished diorama can be the greatest construction, paint , groundwork and layout but if the base on which all that is sitting looks poor, it reflects on the whole diorama. An old picture frame or piece of plywood with molding around the edges dresses a Diorama up and gives it a more polished finished look.
Keep up the good work but put more thought into the layout and the base on your next one.
Cheers,
C.