Zanzibar, Tanzania & Kenya
I visited Zanzibar at the end of November 2023 and dived at Mnemba Island and Nungwi in the north and Paje in the south. The diving is from boats and is very relaxed and easy - shallow sites with minimal current and reasonable visibility. I would compare it to many Caribbean sites - pleasant, and with interesting marine life, but not extraordinary.
Diving is done on the outside of the reef so there aren't really any house reefs or inshore dive sites that you can explore on your own. The main downside is that the diving is very tidal so some resorts get round this by varying the dive time each day while in other resorts you board the boats straight from the resort jetty or are bussed to a nearby beach to walk down into the water.
I enjoyed the diving more in the north more than the south - there were some really great macro sights at Nungwi where we saw frogfish, leaf fish, plenty of mantis shrimps and a variety of nudis. Others, we saw plenty of small and medium-sized reef fish, octopus, a couple of small reef sharks, and some dolphins from the surface.
I would say Zanzibar is better as a beach and relax destination with some diving thrown in, rather than a go-to dive destination
