This was our first cruise with Celebrity so my comments are from the experience on this ship and by comparison with HAL, RCL etc.
Boarding, Sydney International cruise terminal is a great location however it is sadly lacking in quality and efficiency which is a shame.
Cabin, we booked and Aqua Class cabin, 9085 which is under the pool deck but the noise was minimal. The cabin was very good in all aspects, shower fantastic, real towels and as always cabin staff excellent. One issue I personally found annoying was the lack of information on the TV regarding the ships location, where we have been, going to, speed etc etc.