Hi:
One example would be
ShoreDiving.com, a site that acts to meet the needs of those of us who love shore diving. The popular Bonaire Shore Diving Made Easy book is another example, in print, and I liked the Lonely Planet series
Diving and Snorkeling Bonaire book.
Undercurrent is a paid subscription site that posts an annual 'chapbook' with reviews of various sites & operators.
Trip Advisor can be useful for researching some destinations, particularly if you want to look at non-diving activity options, and ScubaBoard is good for reviews of destinations, sites and operators.
Now, let's take a look at what you're considering.
1.) Ideally, it would be nice if such a thing were part of ScubaBoard.com, since that'd bring it a big audience and participant pool.
2.) If you want lots of reviews, you need some sort of online form people can fill out, and to decide what fields to create, and how much different things to have people rate. And you need room for narrative; Undercurrent reviews are a good example.
3.) You need to decide whether you are talking about profiling destinations (e.g. Cozumel), dive sites (e.g.: Palancar Gardens, Santa Rosa Wall) or dive operators (e.g.: Living Underwater, Aldora). In some places, such as Roatan, which operator you dive with has a big effect on what sites you're taken to; on Bonaire, not so much. In Roatan, some destinations make shore diving practical (e.g.: CocoView, Reef House Resort), and some do not. And what about live-aboards?
4.) If you profile destinations, will you cover non-diving activities? This can be a big issue for some people.
5.) How extensive do you want this to be? You say 'the best dive spots in the world.' Do you want only 'top notch,' or do you dream of having every dive quarry open to the public listed? Are you mainly thinking ocean, or do you figure to have freshwater lake diving sites included?
Let's look at some examples.
1.) One could stay at Hotel Cozumel, I assume, book diving independently with Living Underwater, and do all boat dives. Could use steel 120 cf tanks. Might hit a number of different sites. So, is your site going to review Cozumel as a whole, the dive sites, Living Underwater, or Hotel Cozumel?
2.) One could stay at Buddy Dive Resort in Bonaire, do a dozen boat dives up the west coast, & 6 boat dives, while eating out in the evenings. Do you review Bonaire, Buddy Dive, west coast dive sites, etc...?
3.) One could stay at Reef House Resort in Roatan. Do you review Roatan, Reef House Resort of the region of Roatan that's dove from RHR?
You may say 'all of the above,' but odds are you'll have a main focus, such as telling divers where to go (e.g.: Cozumel), where to stay (e.g.: which hotel or resort), who to dive with (e.g.: Aldora) or which sites to dive.
Or maybe you can devise an organizational hierarchy, but it needs to be easy to navigate.
Do you foresee any 'head-to-head' destination comparisons? I enjoy these 'face offs,' because they are what we go through when picking a dive destination from varied options, even though each is special and it's an 'apples to oranges' comparison. How does one compare land-based boat diving in Cozumel to shore diving in Bonaire to rain forest hiking and pinnacle boat diving off Saba to a live-aboard in Belize? Not easy, but this is just what we do when we pick trips.
So yeah, a site that could do all that could be helpful.
Richard.