Beautiful property in a great downtown location
JW Marriott Unioin Square is a pricey, higher end hotel and deserves to be such. This place is marketed as a classy joint and lives up to the bill. The value of the room/service is every bit of $200-$250 per night. If you can find a rate lower than that...take it!
I took BART and made the 10 minute walk from the Powell Street station. I was very early for check in and was accomodated by the front desk. The gentleman checking me in thanked me for my platinum status with Marriott and upgraded me to a corner suite. Very courteous. Status with Marriott also gets you club lounge access. The lounge was very nice although I was never there during meal/appetizer times. 
My room had a beautiful bathroom with stone everything. Closet style shower, tub and toilet were separated from the sink. I remember reading a review where someone said they were charged for using the lotions/soaps/shampoos by the sink...I used most of them and was not charged. The king sized bed was very comfortable. Windows cracked to allow for a breeze. 
The entire hotel staff was quick to open doors, greet you, or do whatever you needed from them. Top notch service here--and you pay for it. Will definitely stay here again if the rate is feasible. Not for the budget traveler. 4 stars.