This is looking interesting!! Looks really cool now but a few simple tweaks could take it up a notch. I've done some sketches hope this is ok! Feel free to tell me to get lost!
What you have looks like its creating a valley shape and I think you could do this better if you put in more perspective and tried to fit most of the rocks in this kind of shape with the blue lines. I'd probably move the small rock in the middle to make that real V shape building perspective.
View attachment 161035
I'd move this big rock to the back and build around it, its quite a different colour to the rest which is a bit distracting and one or two small/medium bits to the front would help it blend in and make it look more natural.
View attachment 161036
One thing that will help with the perspective is getting all the lines or striations in your rocks angled in a way that makes them match, think about a flowing river and how they would erode naturally the flow of the water would wear lines in a similar way but angling them to suit your perspective helps. I've drawn some on here to get an idea - the two top rocks on the right are doing the right kind of thing, both pointing diagonally up towards the corner. Some rocks have multiple directions but if everything around them points the same way your eye will pick up on the ones you want it too.
View attachment 161037
Eg this rock if you rotated it 90 degrees you would get angles running towards the top corner
View attachment 161038
An other thing I think would help the perspective is the small rock in the front, have the front corner I've highlighted pointing to the front leading your eye to the either the top left or right back corners.
View attachment 161039
Something else I'm wondering is how steep is the angle of your soil, it looks quite deep at the front and not sure it raises much at the back? You could lower the front bit by about a third and still be ok and raising the height at the back so its at least 6 inches deep will really add perspective, especially as the plants fill in.
Planting wise what do you think to Dwarf Hairgrass in the front Blyxa Japonica around the base of the rocks and then Juncus and Rotala H'ra as the stems? Some small Buce on the rocks would look good too, or moss, maybe Fissidens?
Wills