I have to admit, Tioman came as quite a surprise to me. Not sure what I was expecting, but it wasn't crystal clear waters and beaches lined with coconut trees and a few huts, which is pretty much what Tioman is. Granted, many of the little resorts are a bit fancier than huts, but not by much in many cases. And then there's the diving. I had set my sights low, hoping that it would be at least a little better than Pattaya. Well, it's a lot better than Pattaya. In fact, in many ways I think I would rate it better than Koh Tao. You're very unlikely to see large pelagics around Tioman, but in all other respects the diving is fantastic.
Almost all of the main dive sites are within a 30 minute boat ride of the resorts along the west coast. Many of the dive shops offer two dive trips in the morning and two in the afternoon. Weather permitting, your surface interval may be spent on a beach somewhere. The most popular dive site seems to be the reef around the island of Renggis. Soyak and the Sawasdee Wrecks are also quite popular.