Houtbaydiver;
I'm afraid Harry's report from a year ago was pretty accurate. In April dove in the Farquahar, Amirantes, and Alphonse groups in addition to the inner islands. With one notable exception (in the Alphonse Group) the diving, for an experienced diver, simply sucked. No fish longer than a meter, heavy bleaching, strong cyclone damage in the south. Extremely disappointing.
One divemaster from Praslin told of watching local fishermen take 85 sharks in one day (I myself didn't see a single shark in the inner islands and only three on the entire trip) and said, "They're killing my livelihood". The islands and beaches are still exquisite, but as far as diving goes...I dove one of the Marine National Parks on Mahe and saw practically nothing. Enjoy your visit, but don't expect much from the diving. I expect you'd be better off in the Bazarutos, Maldives, or even Sodwana Bay. At least there's some protection in those areas.
The same lack of large fish was also glaringly evident in the French Comoros and off the northern tip of Madagascar. The whole western Indian Ocean is being fished out.
We didn't get to Aldabra because the Indian Ocean Explorer was hijacked the same day we were supposed to be there (dodged a bullet, we did). Our local Seychellois guide insists the diving there (protection, remember) is still great...but try getting to the atoll now.
Sad.