The Renaissance Sydney is great. As a Gold member, I was automatically upgraded to an "Harbour Level Opera View" room (or something to that effect - you can easily verify on marriott.com) before check-in - the first time I didn't have to ask for an upgrade at a Marriott. It was decently large, with a stunning view over the Sydney Opera House and the harbour. Note that there is a very tall building between the Renaissance and the harbourfront which presents a bit of an eyesore, but the view is still top-notch.
-Zombie-