Our family of 5 went on a weekday. There was a bit of a crowd but not jammed up...highly recommend avoiding the weekend, we walked by and it was packed. Got. 20% discount by using MasterCard so that was nice.
They are decorated for Christmas and had some Christmas activities which my kids loved. The tanks were bright, and clean, and we even saw Santa scuba diving. My kids really enjoyed the touching area where they could get up close with more sea creatures.
The food options were poor so don't be plan on eating here. Very easy to get around, and stroller friendly (with light crowds).
Overall great 2-4 hour activity. We spent 3 hrs with 3,5,7 year olds. Get your hand stamped before you go up the escalator...its to late after that and you need the stamp and your ticket to go back in. Lots of eating options around the area...although mostly touristy.
If you have kids do this for sure, especially on a rainy day....avoid weekend if possible.