When I was there (Bora Bora)for 2 weeks, 2 yrs ago. The lagoon was so clouded from hotel contruction that you could not do any manta dives with hopes of seeing one. We saw one for about 1 second through the sandy fog. THe divemaster said when he came a few yrs before, you could see many a day. 1 yr before, you could see several a week, he had not seen one in 6 months prior to my arrival.
However, the diving is still nice. You see lemon sharks, I had several within touching distance several times though I did not reach out. Great for photos. Also you see black tip sharks all the time, usually a dozen were in view all the time. There were also clown fish that were great for photos and to watch.
The combination of above water beauty and below water beauty is great. However, I found the diving better on Moorea during my visit there the week before Bora Bora. Moorea is also a lovely place. If you go there, take rent a car one day and drive around.
Both islands are pricey. We stayed at the Pearl at both islands and felt they were the best in both places but also costly. On Moorea, you could walk to the grocery and get bread, cheese and wine easily enough. Its about a 5 min walk. We stayed in the cheapest rooms on Moorea at the pearl and loved them. Stayed over the water on Bora Bora and loved it even more but it costs a lot more.
Bread and cheese and bananas were reasonably priced. Nothing else was...a coke from your room fridge was $5. A local call from the resort was not cheap either at $1 per call. A hamburger at the resort, with fries was $25 for lunch.. did you want a $5 coke with that, sir?
Its the trip of a lifetime with views unmatched... with prices to match all that view.