For our first San Fran trip, we picked this hotel based on recommendation we stay in Union Square. This hotel had a great package deal (free Valet, and food credit) and while still high city-pricing, was a better value than other hotels in the Union Square area. First, a note about location. While the hotel MAY technically be in Union Square, it borders a much more sketchy part of town known as the Tenderloin district. Walk a 2 blocks south, or one block west, and you may quicken your pace a bit. It's ok, just go east a few blocks first before you cut down to Market st for any transit options. Overall a good experience - rooms were clean, neat and had windows that actually opened. That ended up being important because while we could figure out the heat, we could not get the A/C to come on. So had to accept some street noise to get the cool Pacific breezes.
Breakfast - quite good (but expensive) - would recommend at least one breakfast in the small restaurant downstairs.
Valet - also very good - car always there quickly.
Concierge Scott was also helpful - he contacted us before our trip, and arranged for hard-to-get Alcatraz tickets and hop-on hop-off bus package at a price better than we saw downtown. We did have trouble with the bus tix, but Scott got that straightened out for us.
Overall a decent hotel experience for the money, but $100 more a night prob gets you better a few blocks more toward Union Sq park.