Bill's is the most convenient restaurant for those who are staying at the Westin because it's right inside the hotel. Usually, I don't go to hotel restaurants because those have a tendency to be overpriced, but it was a rainy July 4th and I didn't want to walk out to the Strip District so what the hey?
The dining area looked very comfortable and spacious, with two large sections. There's a smaller cafe area out back as well. I'm not sure how and when all those areas are used. For this visit, my friends and I sat at the bar. One look at the menu comfirmed what I knew about hotel restaurants. Everything was premium-priced! However, the Pittsburgher I ordered was easily one of the best burgers I've ever had so perhaps it's worth the cost.
There are a host of minor issues with service though. The server probably expects everyone to open a bar tab. I had to tell her 3 times that I was paying in cash before it sank in. Call me old-fashioned but I don't automatically use a credit card for everything. Secondly, she removed the condiment tray before I was done with it.
In summary, if you enjoy the premium burgers or simply don't want to or can't leave the hotel (like Arkady Balagan in Endgame), I'd say go for it. Otherwise, there are much cheaper options elsewhere.