It's definitely worth seeing! Whenever I bring a newbie with me to Jamaica I always make a point of fitting Glistening Waters into the trip.
Are you spending most time in Negril?
I usually arrange it so that I spend my last night in Jamaica in Falmouth, since it's convenient to the airport that way.
In Falmouth, I stay at the Fisherman's Inn and Dive Resort....it's nothing fancy, but it boasts a quiet setting overlooking the bay and it's right next door to the 'official' Glistening Waters tour operation. I think Glistening Waters charges $20us pp, but offer a discount if you eat dinner at their restaurant (mixed reviews on the restaurant). Glistening Waters herds you onto a big cattle boat with 35 others.
If you want something a lil more intimate and you're a lil more adventurous, the folks at Fisherman's Inn can hook you up with a local to give you a tour. Mooney, a local 'businessman', is your 'go to' man in Falmouth. If you've got a number of people with you, he'll cut you a deal better than what Glistening Waters offers. Mooney can take you to some fine yard food too, places that the locals flock to for authentic good food.
I can dig it up and private message you Mooney's number if you are serious about going.
And just like Ras and marley say, avoid a full moon if you can, and definitely, definitely get in the water....with water shoes, bring your mask and snorkel.........