O was the second Cirque show that I have seen. Mystere was the first. Although O is the more elaborate production, I still prefer Mystere. Can't really say why, sorry. O really is a spectacular show. The staging is very complex. One second someone is walking in a couple of inches of water, and all of a sudden someone dives into the same spot and it's a deep pool. I guess you can say they really mess with your mind. I recommend getting a couple of drinks into you in order to take full advantage of the insane staging of this show.
As far as the "good for kids", I checked off not sure. Everyone knows their own kids, so you need to determine their maturity level. This show is more adult than Mystere or Love, so if you have kids along and are not sure, you might want to go for one of those. (you can read my reviews on both).