Gday Samuel
Not bad at all! (I know it's a double negative;)
The others have touched on a few good pointers. To me it looks a little too symmetrical, especially the trees. Pine + dead tree + Pine. Tank in the centre front. Then three evenly spaced figures. The ground work really looks good, although another thing to observe is the extent to which the whitewash has worn off the 105. This could indicate the end of winter and the thawing of the grounds. Just food for thought on contrasts for the base and AFV. Even if you ran the slope on more of a angle to the base, it would mean the pines' reposition, and subsequent change of view.
You maybe could have had the tank coming
through the trees? The dead tree looks a little out of place, as I imagine the pines are part of a plantation or forest and should only feature like types? could also be talking outta my hat!
Regardless, I hope all this helps you on your way for your next diorama
Cheers
Brad