Seams very heavy on the left side. I think thos is mostly because a large rock is leaning on the glass. I like the sharp jagged piece creating a ledge. It seams as if the rocks are pushed to far into the corners or to the back. If the substrate was shallower in the front it may give it more depth too. Just my two cents. Hope it helps.
Perhaps move the left grouping a little to the right so there is some space between it and the glass (you'll be grateful once you have to clean the glass). Then maybe bring the right grouping of rocks a little bit more towards the midground - this way they will look larger so the layout is better balanced. Also you will gain some more depth to the layout.
Just so ideas
When I laid out my iwagumi I fiddled with it a bunch and took a ton of pictures. Then I compared all the pics and went with the best one.