Not so much on the left side. I more mean that the substrate seems to slope down at the back if anything at the moment. Especially in the area you have the 'gap'. If you raised the level at the back so it slopes up instead of down I think it would look bigger.
Maybe (if you don't want to add more substrate) you could fill the deep back section with normal gravel in a nylon stocking to save your substrate.
The LHS at the moment plateaus where your top driftwood and rocks are. Maybe it needs to be more of a slope front to back.
I like the way it is high on the left and dips then goes back up on the right. So you would have to raise the level at the back all the way along.
Hope this makes sense.