I think it depends on who you go with. This is my second time to the Blue Hole and I really love it. The structure is amazing and the experience of swimming between 20'+ stalactites is unique. (At least in my limited diving experience.) If all you like to see is coral and fish, you'll find it underwhelming. If you enjoy seeing beautiful rock structures in a unique and interesting way, you'll probably love it. Like any boat diving, the size and approach of the outfit you choose to go with makes a huge difference. Both times I went, we used Belize Diving Services out of Caye Caulker. Modern Newton dive boat with a smaller number of divers (10 last year, 14 this year - split into two groups) and really early start making us the 1st or 2nd boat of the day make a big difference in the experience. I would probably hate it if I did the dive with 30 other divers in the water and multiple boats present.
-Matt