We were staying at the Fairmont, so we did our diving with Dive Bermuda, which is located at the resort, but conveniently also gets excellent reviews on TripAdvisor. We were originally supposed to dive the first three days that we were there (Sunday, Monday, and Tuesday), but Sunday's boat was cancelled due to weather. We walked down to the dive shop (which is on the beach) and despite Rob's whining to the contrary, I think cancelling the boat was definitely reasonable. It was insanely windy; it was unpleasant to just stand on the beach, so I don't think we'd want to be on a boat in that weather. We ended up diving on Monday, Tuesday, and Thursday instead.
Each day, we did two dives with the first dive on a wreck and the second dive on the reef. The sites were roughly 5 to 15 minutes from the dive shop, and we generally returned to the shop between dives, either to drop off or pickup divers (the second dives were shallow enough for discover scuba or open water class dives). The boat is anchored right off of the beach, and after getting into our wetsuits, we waded/swam out to board the boat. Our gear and anything we didn't want to swim out was sent over on a kayak. The boat was nice and spacious, and well laid out (random fact: it's the same kind and size of boat as the old Monterey Express), and all of the crew that we dealt with from the shop or boat were helpful and competent.
The water was quite chilly while we were there. I brought a brand new 5mm wetsuit, and decided while packing that since my suit was brand new, I didn't need to pack my vest. That was a big mistake :) The water temps were in the low 70s, which made for a chilly second dive everyday. On the first day, when it was overcast and chilly on the surface, it made for a borderline too uncomfortable to dive second dive. Apparently the water temps increase quite a bit in May, so if we'd come a few weeks later, it probably would have been a lot more comfortable. Anyway, we sucked it up and managed to do all of the dives, but if we were not visiting Bermuda for a work event with fixed dates, I would definitely go a month or two later.
Their staff to diver ratio was really impressive too. Our guide for all of our dives was Kwe, who was great (and who we shared with between zero and two other divers throughout the trip). Once he decided we knew what we were doing, he pretty much let us do what we wanted, even if it wasn't exactly in sync with the dive briefing of what we were supposed to do :) He also took us through some pretty cool swimthroughs on one dive, and was helpful at giving Rob suggestions for what to photograph, and setting things up so Rob could get some nice silt-free shots of the best parts of the wrecks before the rest of the divers showed up.
Overall the diving was better than I'd expected. The reefs were covered with invertebrates like sea fans and gorgonians that were in great shape, but there wasn't a lot of variety. So as you looked along the reef, the life was lush, but it was the same couple of tannish-pink gorgonians and purple sea fans over and over again. There were also very few fish. The guides blamed this on lionfish, and several of them (including Kwe) carried spearguns to spear any lionfish that we found. He speared a few throughout the week. The wrecks that we visited (whose names I don't recall) were in varying states of collapse. On the first day we visited one that was really just bits of wreck; on the second day, we visited a totally intact wreck (which I believe was sunk intentionally); and the last day, we visited a wreck that was broken in two, but had two really cool paddle wheels that were intact, one which was laying on the bottom and one which was standing up. That last one was my favorite wreck.
The reefs that we visited were basically just different spots along the barrier reef running along the south side of the island. A couple of the sites had swimthroughs running through the reef, and one had some really neat, long swimthroughs. That was relatively amusing.
All in all, we had a good time and it was definitely worth bringing our dive gear since we were visiting Bermuda anyway. And if you are there, I'd recommend Dive Bermuda (which has a second shop on the other side of the island too). But I don't think I'd recommend Bermuda as a standalone dive destination.