Denny knows much more about North Ambergris than I do, but I have to jump in and say that based on my experience editing or writing several guidesbooks on Belize and with Belize First Magazine, that Captain Morgan's -- like Denny's former employer Journey's End -- is one of those places that gets mixed reviews. Some like it; some don't.
There are some hotels in Belize, in all price ranges, that get almost universally good (or in a few cases bad) feedback, but Captain Morgan's is one that gets a mix of reports. Just use the search facility here on this board, and I think you'll get a sampling.
I think one reason is that this property has gone through a number of management changes over the years. It was run by a wholesaler and his son for awhile, then another group, then a couple from Belize City, who didn't last long, then there was another change or two. At one point the property was put up for sale, then it went into its condo development phase. It just doesn't have the consistency of management and mission of some of the best places on the island.
Personally, I've stayed there and enjoyed it, but on subsequent visits I haven't always gotten the impression the on-site management really was on top of things.
Belize books and publications by Lan Sluder:
Belize First Magazine http://www.belizefirst.com/
Fodor's Belize and Guatemala Guide
Belize First Guide to Mainland Belize
Adapter Kit: Belize
Fodor's UpClose Central America
Belize Book of Lists 2000
San Pedro Cool (coming soon)