Just got back from St.Lucia last Saturday. We stayed at Sandals Halcyon and had a great time. We did all of our dives via all inclusive type deal with Sandals. Their dive outfit is O.K. Nice boats and friendly crews. They are a little too conservative on bottom times for me but not bad. Air hogs in the group kept bringing me up with 1100 to 1500psi. The afternoon shallow dives are nothing to write home about (Bay of Pigs). But the regular morning dives were great micro reef diving (Pitons area).
We opted for the extra $100 each day trip to Martinique and absolutely loved it. It included the hour boat ride, two tank dive trip (great diving), good picnic type food on the boat, a few hours shopping on the island, and free beer after diving and on the way home.
A word of warning...If your dive log is not present before your first dive with them. Or you have not been diving in the last 6 months. They will make you do a check-out dive in the pool. No big deal really. All you have to do is don your gear underwater in the pool.
The water off the beach at the Halcyon was a bit turbid because we got there after some pretty serious rain. The beach was ok though. You can always transfer to their other two resorts. The Grand and the Regency. Both have clear beach water but these resorts are a little too Disney Land polished for my taste.
I think they are still running their half price gig. They also have a full blown hurricane guarantee.