We have just come back from the Hamilton Island cruise on board the Aria. Having been on the Pacific Dawn twice in the past five years I was keen to see what the Aria had to offer.
It is a smaller ship, which I didn't find to be a problem. There is just one trick you have to learn: getting across some decks requires a walk up and down a set of stairs - tricky - but you get used to it quickly. (being handed a little pocket map upon boarding helped!)
We found the Waterfront to be a pleasant a la carte experience. The menu offered a good variety and everything we ordered was superb. It was a shame that you couldn't book (like on the Dawn) but you could drop into the restaurant and they give you a pager and you can just grab a drink or take a walk while you wait - a good option if you weren't in a hurry (to see a show etc.)