I'm a newbie snorkeler. I saw a lot of different fish but these are the sightings that thrilled me the most on our last trip:
We saw a green murray eel when we snorkeled at Catcha Falling Star. It was on the bottom of the ocean floor and it kept sticking it's head out of the coral to look around. I was absolutely captivated.
We also saw a Lesser Electric Ray. It was swimming along the ocean floor in front of Banana Shout.
These were both new experiences for me. This is was my first time seeing an electric Ray or a Murray eel outside of an aquarium.

I'm hoping next time we can go out with the Famous Vincent and see more.
I think we'll also check out the reef beyond the old Negril Yaught club to see if that reef you described is still intact. That sounds very cool!

Didn't see any sharks or dolphins though....