I was there once and found the atmosphere fun and the food fine. One thing that put me off was that the waitress pushed the high-end sakis and expensive special without mentioning price.
I was very disappointed by O Sushi. There was an odor to the place and fruit flies flying around the bar. Sushi was OK...would have had to been outstanding to overcome cleanliness issues.
Perhaps another reason to avoid hotel food in general?
I've always found it decent if not a little pricey (but hey, you're in a Westin) Stick to the nigiri and shashimi. I find Douzo trying a little harder to be hip than to serve great sushi, but I think I'm in the minority here.
their presentation (e.g., spider maki) is better than Douzo's, but since Douzo opened, we've gone there instead because they've got more interesting rolls...e.g., red spider maki, snow mountain, etc.
I think the sushi is OK, but overpriced. I would opt for Douzo less than one block away for a much better all around experience and some very fresh fish.