I haven't stayed at the S-La in Sydney but have the island S-la in HK and had a very comfortable stay. I would imagine the Sydney one would be of a similar standard. We stayed at the IC a few months ago and had a great suite with views of the Bridge Opera house and the Harbour to the East. The Club lounge is on the top floor and has spectacular views. Don't forget to book through Virtuoso if the hotel you choose is part of the programme - the IC is and I imagine the S-la is too. Gets you free Club access at the IC - not sure what the benefits are at other hotels but usually at least free breakfast and an upgrade if available. If you don't know a virtuoso agent - there a few who post on here.
The trick with Tripadvisor is to read the reviews selectively. Ignore any that are 1 time reviewers only and concentrate on those from reviewers who stay in similar class of hotel to you. Also look at the photos.