People also talk about the diving at Cayman Brac and Little Cayman. Grand Cayman is a popular destination, with a rep. for being pricey (like with food). It might help folks advise you to better understand your frame-of-reference.
1.) You've got a bunch of dives, but where? What are you comparing it to, potentially?
2.) Do you plan to stay at a land resort/hotel & go out daily on a 2-tank dive boat charter, or do a live-aboard, or make a one day stop as part of a cruise ship excursion?
3.) Do you mainly do boat dives, or is a shore dive important?
4.) Do you need non-diving activities like casinos, night life, nature hikes, etc...? Are you traveling with non-divers who need these things?
5.) Are there other places you're considering going that you might want to compare it to? Such as Bonaire, Cozumel, St. Thomas or St. Croix?
I had a 2-tank cruise ship dive excursion in Grand Cayman & enjoyed it quite a bit.
Richard.