As a Diamond, you should get an upgrade to a room on the Executive floors - and regardless, will have complimentary access to the Executive Lounge for your room occupants.

The lounge has a nice breakfast buffet (western and Asian selections), tea/snacks in the afternoon, and cocktails/light bites from 5 to 7 pm. As an option to breakfast, you can also take breakfast downstairs in the Cafe (which is good if you are traveling with others who don't have Executive Lounge access).

You get complimentary fitness center access too - and a few other odds and ends. Sometimes they bring up welcome tea when you arrive - but not always.