I like it! One thing to keep in mind though - in an iwagumi scape the rocks should look as if they were shaped by the flow of water in the tank. Since you have a powerhead in there, I would re-position those rocks such that the majority of rock is angled with the flow of the powerhead. Switching the two rock outcroppings and angling the large rock that is currently on the left with the flow of the powerhead would achieve that look.
Keep in mind, though, my criticism is really splitting hairs! That's really the only criticism I could come up with and it's perfectly fine to leave it as is since it looks great. Up to you.