Diving the Great Barrier Reef
Unfortunately many parts of the reef are not well protected. For example, around the Whitsundays, a lot of the coral is dead, with day trippers walking on it and damaging it, and a resort permanently anchored to the reef itself. It was very disappointing to see.
However, Queensland redeemed itself for me when I dived the Yongala, out of Townsville. I would rate it as one of the top 10 dives in my (long) diving career.
It's a wreck, so has a fascinating history, however although it's a wreck dive, the real appeal lies in the life that surrounds the wreck. It's an eco-system in itself, all condensed around the wreck, from small critters to very big pelagics, and just about everything else in between. The potato cod are enormous, the sea snakes many and varied, and the turtles looking every bit like those on Finding Nemo.
In terms of reefs, Ningaloo Reef on the west coast is much more pristine. Little point in diving it - it's too shallow! Just snorkelling is amazing. Again a huge variety of life, including the ubiquitous white tip and black tip reef sharks, turtles and rays.
I would skip the Great Barrier reef, head for the Yongala then over to Ningaloo.