Belize is truly great. I might suggest you take a look at Turneffe if you are looking for luxury, great snorkeling and getting away from it all. It doesn't get much quieter out there. We've done San Pedro/Ambergris, Turneffe, Glovers, and now spend alot of time in the Bay Islands. The macro photography is arguably the best out at the Atolls followed by the others, but with great buoyancy control and a patient eye, the reef will come alive.
All of that said, I would temper your expectations if you are looking for Pacific quality macro/reef life. We have done Indonesia/Raja Ampat/Bali and Komodo recently and there is nothing in the Caribbean that matches the reefs or creatures there. I am not bashing the Caribbean, we spend alot of time there these days and love it, just understand that its different.
Have a great trip!