We went there when it was very crowded. The problem starts at the entrance, where the queue to get in advances way to slow. A lot of people have an e-ticket, and could just enter after scanning the ticket (like in most other places that have e-tickets), but that is not how it works here, everyone has to queue.
Once inside, we wanted to eat something, and the cafeteria was also in chaos due to overcrowding. They really didn't handle it efficiently. Also, the cafeteria was somewhat confusing, and was missing instructions (it was not very clear where to queue/order etc). The food offered (cafeteria and stalls outside) was almost entirely junk food, which is a shame.
The actual "main attraction" of the sea life, the animals etc, wasn't too bad. It's a bit limited and I've seen more impressive places elsewhere, but it's ok.
If you're in the area and it's not crowded, you can have be a nice (but short) visit.More