As far as warm water goes, I've dived Coz, the BVI, Australia and Indonesia, and Maui and a couple of dives off the Big Island.
Hawaii diving is hard coral, and not very colorful. The big attraction is that many of the species are endemic to the islands. You will not find soft corals or big schools of fish (or at least, over four years, I haven't). You will find turtles and reef sharks, and I was fortunate enough to dive with a monk seal, too (although that's one dive out of many).
The shore diving reefs off Maui are often not in very good condition, and I have seen them deteriorate over the last five years -- it's sad that the change is great enough that I can see it, but it's also been documented by official studies.
It's warm water, and access to the ocean is easy and there are many shore diving sites. There are good charter operators, and my favorite, Mike Severns, has shown me some animal which are rare even in the islands.
Still, if I were going to spend limited vacation time looking for a mind-blowing diving experience, it wouldn't be in Hawaii. JMHO.