Going here as a kid, I really liked this place. I didn't notice anything about cigarette smells, dirty rooms, old furniture, whatever. The place has an awesome adventure dome, awesome restaurants (from my perspective, the mozzarella sticks at Pink Pony were fab) and it's huge. And it's in Vegas. If you have kids, I recommend Circus Circus, because trust me, they will not care about the aforementioned flaws. They will care about the awesome things.
Best part: one of the ticket machines broke down in the adventure dome, so we went and got a staff member to help out. As he was fixing it, a whole bunch of tickets came pouring out (a malfunction of the best degree) and the guy gave them to me to keep! I didn't even have to play games to win them. Just got them for keeps, just like that. So off I went and cashed them in for an oversized stuffed animal (a dog, just for those who are interested), and it still sits in my room, I can see it as I type this.
And this is why Circus Circus rocks.