The manta rays are as spectacular as everyone says the are... if you get to see one! Ours was the first tour of the evening, so the sun was just barely setting as we got out on the water. The manta rays don't usually show up until it's dark, so much of our time on the water was spent waiting and HOPING that the rays would show up. The finally did, just minutes before our time on the water was ending. We saw about 4 manta rays make slow passes below us, and then in one glorious ending, a manta ray spun up towards us. The luckiest groups see the manta rays spin over and over beneath them. I feel fortunate to have seen it once.
Honestly, the first tour group of the evening is not the best spot. I didn't know that at the time-- we took what we saw available. But in hindsight, I would recommend that people wait until a time when it is completely dark. Your chances of seeing the majestic rays is certainly higher. It's a bit sketchy that companies are offering a slot that happens BEFORE the sun is all the way down.
That being said, our guides were knowledgeable and lovely people. We had an overall positive experience because THANKFULLY we did get to see a few rays at the end.