We came by during the night to watch the display. It comes on every 15 minutes or so. Its completely complimentary, courtesy of the Bellagio.
The crowds of tourists it brings are great if people watching is your thing. Music is pumped from a loud speaker and the water and lights are blasted in sync with the beat. We had no issues lugging our stroller and infant up beside the railing to watch.
It only lasts a few minutes but it is extremely beautiful to see. Our 6 month old enjoyed being held and watching the show. Most of the crowd watching fall silent and it's a wonderful moment to be in...the center of such a busy urban environment with everyone swirling around and several hundred people quiet and still just watching the water.