It's pretty cool that the Bellagio has an art gallery. I've been here twice now. The first time for the Monet exhibit, and recently for the Andy Warhol exhibit.
Although it's small, they do showcase quite a bit of work that's familiar and plenty that isn't. Both times there were pieces that I recognized, and others. The Warhol one of Elvis was cool. I liked that and I'm not really an Elvis fan. The price of admission includes the audio so make sure you get it. It gives some cool insight into the piece you are looking at.
It's probably going to take about 30-45 minutes depending on how quickly you go. It's not tiny where you'll be done in 5 minutes, but it's not large either. So, enjoy the art and audio!
The only thing that really deducts a star is the price. Unless you have a military discount, or locals discount, it can be pretty pricey in my opinion. We went on a Wednesday and it was $8 otherwise, it was $13.