It's not often that you can find a gallery that exhibits art from some of the most renowned artists of all time. I'd say most people's opinions will be based on what the exhibit is at the time, however the gallery itself is a nice change of pace from the stereotypical Vegas life.
The gallery itself is not very big in comparison to others out there ,but what do you expect? It is after all in a hotel. However, what other gallery around will give you the opportunity to see an original Picasso or Monet?
Despite it's size, the gallery does offer an audio tour headset that is optional that will guide you through the pieces on display and give the history behind them. You will have to check in any camera or plastic bottles before entering (although if you have a slim camera you can get it in, just don't expect to grab any shots without a guard coming down on you).
It is $20 to get in, which I think is pretty pricey for what you get. If you're a big fan of art, it could be worth your $20 to see certain pieces. The best bet that I'd suggest is see it if you're a guest of the hotel and have a weekend package that will include tickets to the museum.