If you're child free, this isn't really an obvious choice for Vegas entertainment. But we decided to stop in because it was my SO's first time in Vegas and she wanted to see as much as possible. Also she doesn't gamble or drink so yeah... we had to find some other things to do, right?
Anyway, this is a fun place to wander around for a little bit. We arranged our visit to see the first circus act of the day - a (blessedly brief) clown show followed by a pretty impressive solo trapeze artist. The show started at 11:15 AM and was already packed with families so I wouldn't even want to think what the later shows are like. But we enjoyed the 30-minute performance.
Circus Circus feels so old-school Vegas, which I like. BUT, this is clearly the place to stay if you're packing kiddos - the place is lousy with 'em. The arcade and the amusement park rides are fun to check out briefly if you're into that thing and CC isn't too inconvenient from where you're staying (it's at the far end of the Strip).