Great Location and Comfy Rooms
We stayed here for 3 nights with several other couples and all of us had a great experience. First off I have learned that travel websites aren't the cheapest route to go...we booked directly through the Hyatt and ended up changing our reservations 4 times because we kept finding better deals directly through them. That may aggravate some people but I check that kind of stuff all the time so I love it that you don't get penalized for making changes.
Anyway, we went from $229 a night, down to $170 a night, then to a special where it was $209 a night but if you stayed 3 nights you got the third night free, plus breakfast for 2 each morning. So in the end we felt like we got a great deal. The hotel is right at Union Square, easy walk to trolley and BART. Nice location for shopping and dining. The rooms are accurately represented in posted photos. Not super huge but very chic and inviting. The bed was very comfy, there was a small fridge, coffee maker, bathroom well appointed and modern. No complaints at all. Maid service was very prompt in the mornings, we ate breakfast at the hotel restaurant every morning and it was wonderful. Servers and everyone we encountered were very friendly and helpful. 
In general San Francisco is a VERY NOISY place and I was woke up several times by trolley bells ringing but I didn't feel that was something the hotel could control. The lobby is currently being renovated but that didn't impact anything we did. Actually didn't hear any noise coming from there. I would stay here again and would definately recommend it to others.