This water show in front of the Bellagio has become one of the quintessential things to do while you are in Las Vegas. It is absolutely free and is not something you should miss.
The 100 + water jets are synchronized to classic Las Vegas show tunes and Frank Sinatra songs. At night, the songs and water also include different colored lights which can be really dazzling.
While this show can look really neat when you are driving by on the Strip, it is really something that you should take the time to see in person on the sidewalk.
During the weekend and busy times they run a show every15 minutes to half hour. So if you have the time it is worthwhile to watch one or two shows because there are many different ones that play throughout the day and night.
The area has also become popular with sidewalk musicians, performers, and other characters you can take pictures with. So there is more entertainment than just the show. I would totally recommend making it one of your stops while you were in Las Vegas.