My 15-year-old daughter and I both enjoyed this experience a lot! Around 9pm, our kayaking guide, Hunter, picked everybody up near Friday Harbor and then drove us in the early twilight to a nearby bay. He provided us with a brief overview of kayaking and the equipment, after which we set out in the two-person kayaks.
The first hour or so the sky was bright enough that the water looked pretty normal. However, this allowed us to familiarize ourselves with the kayaks before it became really dark. By 11pm, though, it was dark enough to really see the bioluminescence clearly, and we found it quite magical! Sometimes a stroke of the oar would yield swirls of many tiny blue-white glitter, while other times a stroke would cause fewer but larger points, and sometimes a stroke would have no effect at all! (This unpredictability added to the experience.)
Once the sky was dark our guide also pointed out the North Star and a few constellations.
I was quite happy with the experience overall. On our outing there were eight guests with a range of experience and physical shape, and Hunter was able to accommodate everyone. (I had been canoeing several times in the past, but had not been in a real kayak before that night!)
My daughter gives the experience five stars. I would give it about a four and a half.
Hints: 1) We went when the moon was not out. This probably helped make the luminescence more visible to us. 2) Your shoes will get wet! You might want to bring a spare pair for the trip home.