Hotel Adagio is in a good, but not great location across from the Curran Theatre on Geary St. in San Francisco. This area is technically still Union Square, but once you hit the theatre district you are closing in on the Tenderloin, which may not sit well with some folks. Personally, I don't see this as a major issue. The heart of Union Square is just a couple of blocks down Geary, and though this area of town may have a high homeless population, the truth of the matter is the entire city has a homeless problem, so the best advice is to get prepared to be asked for spare change before you arrive in San Francisco.
The innards of the hotel are extremely well done. The lobby is spacious, sleek, and clean, but not a giant wasteland or a tiny closet. Many JDV properties tend to have tiny lobbies, but Adagio does not have that problem. The rooms themselves are fashionably boutique, and the décor is swanky yet tasteful. My room was on the top floor (16) and was larger than the standard boutique hotel room. The room also offered sweeping views of SF from two different vantage points.
The service at Adagio appeared to be up to snuff. Rooms are equipped with Ethernet ports, and when I asked for a cable at the front desk I was quickly and courteously accommodated. Room service and housekeeping were also above average.
Hotel Adagio is a fine choice in the hotel littered Union Square district of San Francisco. The property is a couple blocks from central Union Square, a short distance to the Powell Street train station, and close to the Powell Street cable car stop. If you are looking for a swanky boutique hotel with good size rooms, check this place out. However, the location of this hotel does put you on the edge of the Tenderloin, and even though this property recently completed a stellar renovation, it is still an older building working through some kinks (read temperature). If either of those factors are troubling to you, it may be time to look elsewhere for your lodging needs.
On a final note, like myself, you may see photos of wonderful looking Adagio terraces on sites around the web. Terraces overlooking a city are one of my favorite features at a hotel, and one of the first things I did upon arrival at Adagio was ask how I could get to their outdoor terraces. The staff informed me that the two terraces were attached to the two suites on the top floor of the hotel, and that they were not for all hotel guests, just suite guests. Needless to say I was a bit disappointed.