This is a busy, business hotel with a noisy lobby, but it's in a perfect location for Union Square, shopping, theaters, etc. We were there, coincidentally, during a tech conference so I'm not sure if it is usually as crowded. We were first impressed to learn that we were automatically upgraded to one of their more spacious corner rooms which afforded us great views of the city. However, we told that we would be called between 3:00 & 4:00 when our room was ready. We never received a call and didn't get checked in until 4:30 which was inconvenient as we had a 5:00 dinner reservation before an early show. Once checked in, we found out that the light in the bathroom over the sink was not working. We immediately reported it, but it remained unfixed the following day. We were also supposed to have a refrigerator in the room, but didn't. I will say that the hotel checked to see how our stay was going - not too good - and they immediately responded to our concerns and also compensated us for our troubles. We had booked this hotel so that we could enjoy the View Lounge on the 39th Floor, but it was closed one night due to a private party - very disappointing for hotel guests. The day we checked out the hairdryer stopped working.
The concierge service was great, and unlike comments of long lines from others, we did not have to wait long. As Elite Marriott members, we were expecting a continental breakfast, but were pleasantly surprised with a full cooked breakfast. We also enjoyed their appetizers later in the day which could have been dinner if we didn't already have dinner plans. Desserts were served until 10:00 and drinks were on the honor system in the Concierge Lounge.
We will definitely consider staying at the Marquis on a return visit to San Francisco, but hope that next time we will experience better all-around service.