I haven't stayed at the Negril Beaches resort, but I had a chance to visit the resort while staying at the Sandals down the road from it.
We did 3 days of 2 tank dives until a storm came in the last couple of days we were there. The diving is nice, and usually ranges from the 30' to 90' range for most of the dives there. Our first dive we ran into a sea snake within 30 seconds of descending. Great experience. Most of the dive sites were within 1/2 to 1 mile from the resort. We would often do a single dive, come back to shore for lunch, and then head back out on the afternoon boat. If you timed it right, you could probably do 3 dives a day.
The diving was mostly reef dives with a few swim throughs and a nice fish feeding dive one day. The reefs back in 2000 were bouncing back quite nicely from over fishing. My understanding was that Jamaica was putting forth quite a bit of effort to re-establish the reefs and fish populations. From what they told us on the boat, the government banned the practice of tossing an anchor on a reef, and went through a lot of trouble to establish permanant lines to anchor off of.
The food there is incredible, and is the primary reason we went to the Beaches resort. We spent an evening at the Beaches, and it was a stark contrast to the couples only Sandals resort. There were family's every where, and the place seemed to be completely designed to accomodate everyone. There was an arcade that we walked by, tidal pools, fun stuff on the beach, and other stuff like that.
The only thing I didn't like about the whole experience was the drive to the resort. The flight for us was from Ca to Fl, and then on to Jamaica. Needless to say we were pretty wiped out upon arrival there, and the bus ride to the resort was an experience I'll never forget. I didn't get sick on the ride there, but I was pretty close to losing my lunch.
The country side on the way to the resort is absolutely beautiful, and by the time you get there, you have a strong realization of how remote Negril is from the other major cities on the island. The disturbing part is how crazy the laws of the road were in Jamaica. The bus driver would pass anyone, any time he felt like it, and there were several times that, from our perspective, would be considered close calls. The odd part was that as long as you did like the locals, you were safe. The only people in car accidents along the drive were European / American types who had clashed with local drivers. Not sure if it was a scam (i.e. insurance claims), or if the foreigners were the cause of the accidents.
I've had the opportunity to drive in a few different countries over the years, and this by far was the most nervous I'd ever been in a car. That's saying something considering my time in Saudi Arabia back in the early 90's with the U.S. Army.
If I did it over again (and I would definitely do it again, especially with my family), I would look into the puddle jumper between the main city and the Negril resort. It might cost a bit more, but the 1 1/2 to 2 hour drive took more out of me than the flights did. The resort, the service, the hospitality, the diving, and especially the food was perfect during our stay.
Hope this helps.
~ Jason