Vanuatu is well worth a trip. Wonderful friendly people, lush green tropical jungle, great weather, interesting history, WW II relics, caves, freshwater pools.
All I can tell you about is the reefs in the neighbourhood of the Coolidge, near Luganville on the island of Espiritu Santo.
The reefs are nothing special. Large variety of coral species but the visibility is often poor. This is in a tidal channel with rainwater runoff. Plenty of food for corals and anemones, but not great for photography. There are too many storms to allow big gorgonians to grow (this also applies to the Coolidge except in sheltered corners).
Million Dollar Point is a fantastic photographic opportunity. There are hundreds of large vehicles and a few wrecked boats all piled up on a slope from 9 to 40 metres. Wide-angle paradise.
I didn't see any pelagics at all. There is reputed to be a single whitetip reef shark on the Coolidge.