We just got back from Long Island. I'll be posting a more detailed trip report in the next few days, but a little bit of info...
I was very impressed with the diving there...I wasn't expecting much because I couldn't find much information. It's not a diving destination, per se. Not in the same league as Cozumel, Cayman, Bonaire, etc. But, it was a nice change and we say plenty....very pretty. We stayed at Stella Maris resort. You can rent a vacation home via the resort or privately. Or, rent a place elsewhere on the island and just get yourself to the marina. Rental cars are extremely pricey though, so this is a huge budget consideration.
The Stella Maris watersports team seemed a little disorganized, but Robert, the main divemaster knew his stuff and they were very focused on safety. A little bit of confusion one day about which boat they were going to take and they didn't have spare tanks or o-rings on board when we switched from their normal boat to one they charter, so bring a save a dive kit if you go.
It's nothing like the diving in Cozumel. Basically, the coral rises up in large heads from great seas of sand. Quite different from other diving we've done, which has normally been walls. For the most part, large schools of fish, and lots of my favourite reef fish...french angels, blue parrotfish, rock beauties, etc. We did quite a few swim-throughs. Most dives had a shark or two hanging around. There is a possibility of also doing a shark feeding dive, a 100ft wreck, Dean's Blue Hole or a trip over to Conception Island for pristine wall dives (only way to go diving there unless on a live aboard or have your own boat). We really wanted to go to Conception, but they needed a min of 5 divers plus excellent weather. Didn't work out.
The island itself is kind of interesting as there is Dean's Blue Hole, tons of secluded and beautiful beaches if you want to go exploring on non-diving days. But, there's not much going on in the evenings unless you want to visit a local hang-out...very laid back and relaxing.