We like this restaurant. DD8 loves this restaurant. It is her absolute favourite restaurant at Disney World. We had dinning plan and have eaten at CRT, BOG, etc., and Coral Reef is her absolute favourite!!
She told me that she thinks it is very fun to sit next to the fish tank to eat. It's a kid's perspective. We sat once right at the tank and once at the semi-circle table facing the tank. Just happened to be that way, we didn't request it.
I think you can request upon check in at the restaurant (it doesn't hurt to ask, I reckon), but maybe it will take longer to wait for such a table.