Pleasantly Surprised
I picked this hotel to save a little money on a last-minute stay in the city. It was just me, and when it's just me, I'm willing to rough it a bit to save a buck. Truth is, I simply needed a place to hang my hat between two days of appointments near Union Square, and the hotel where I usually stay, the Grant Plaza (which is much closer to Union Square), was fully booked. 
I'm quite pleased to report that the Monarch, though quite old, turned out to be quite functional and a good value. My room (#408) was clean, quiet, and in good condition. The bed, though not outfitted to the Hampton Inn level, was comfortable and functional enough for a good night's sleep. The bathroom was basic, but clean and well-lit, and there were plenty of towels. The room was equipped with an iron and a hair dryer. The free internet service was slow and intermittent but given the price, I said what the heck.
The Monarch is about seven blocks up a modest hill-climb from Union Square. No sweat for most but I'd be concerned about the incline and the distance if I had an elderly person or someone with health problems along. The neighborhood around the hotel is unremarkable at best, and there's some riff-raff a two or three blocks away on the side streets. None of this is in-line between the hotel and Union Square and I never felt unsafe. You'll want to walk down to Union Square or take a cab somewhere if fine dining is on the agenda, otherwise, there are a few diners, dive bars and small grocery stores nearby. 
The hotel is also just one block off of Van Ness Avenue, which is Highway 101 through the city. The point here is that because it's easy to find and navigate 101, you don't need an understanding of the layout of SF and won't have to contend with a lot of crazy traffic. Just keep in mind that Geary Street is one-way, so from Van Ness you'll need to take Post or O'Farrell a block or two, then circle around and come back up Geary. 
I noticed that the hotel is AAA-recommended. 
I'd stay here again.