I'd get some more live rock, take that background out and paint it blue or black.
I'd stack the rocks high on each side leaving a cave on one side low near the sand bed. On the other side leave a cave towards the middle and leave the center open.
This is just my opinion. Tank looks great though and it's all about what you like not what everyone else like. Make the tank unique and yours.
I just offer my options and my opinion as I'm very anal with aqua scaping.
I mean no dis respect
EDIT: agree with above poster. Your gonna want more flow.