I've heard that the Sirens show doesn't compare to the old pirate show they had before, but having nothing else to compare it to, it was one of my favorite free shows on the strip.
Not for kids, although seriously who brings their kids to Vegas anyways, the city of sin, strippers, gambling and all kinds of vice? The show is fun and cheesy. Its very Vegas with scantily clad "Sirens" on one pirate ship dance and sing to the pirates on the opposing ship luring them into a fun battle scene complete with pyrotechnics.
Get there early and get a good spot because it gets crowded quick (the bar in front of TI has comfy couches to sit and watch the show VIP style free of the crowds).