The casino area was the worst of all I encountered. It actually smelled so bad I had to wait outside for an hour for my friends to finishing wandering around. I dodged back in twice to check the score of the Cubs game, but basically held my breath at the gaming area the entire time. It was pretty gross.
Perusing reviews, it appears that some of the toiletries smelled nice, so I imagine if you walked around the casino with some of those shoved up to your nose, you wouldn't even notice.
Outside though, I got to watch the water show at the Bellagio twice, so I was glad I could enjoy it.