I just dove in Zanzibar, Tanzania after a Maasai safari in Kenya in April. Flew direct from Nairobi to Zanzibar. I stayed 2 nights in Stonetown, then 5 nights in Pwani Mchangani at a place called Mambo Ocean Resort. Nice place, about $50 USD per night with aircon. I dove 3 days with Scuba Blue. Marine life was good but no big stuff. Several reefs were badly bleached but one called Leon's Wall was excellent plate coral and very healthy. I dive with my own equipment. The shop owner is very competent but their facilities are limited. I think the diving there was worth doing because I was close by in Nairobi, but I wouldn't plan a whole vacation around Zanzibar diving, from what I saw. However, the beaches and small resorts make for a very nice vacation destination. LMK if you want more info.