It's very nice. I'd probably slope the substrate back to front, and a little side to side. Differing heights adds extra dimension to the scape. Also, bumping back the cave and rock formation a bit (and elevating one of the above the other - I'd suggest the rocks) will give the tank a bit more of a "feel". Tall plants in the back, like vallis would be nice, and maybe some moss on the cave to 'blend' it a bit.