I stayed at 24 Henry 3 times and that's the only place I consider staying at when going to San Francisco.
The location is great. Bus 37 to Twin Peaks is 5 minutes walk from the guesthouse, and it's in the heart of the Castro (gay neighborhood, vibrant, good night life, extremely safe). You can also walk to the Mission (10 minutes walk) and to Haight Ashbury. Also, streetcar F is a few steps from the guesthouse.
The prices are really very reasonable for everything you get (SF is expensive). The rooms are very comfortable (I stated in 3 of the 5). Each has its own style. The Mural room is especially lovely. Sure, some people will tell you that the house is a bit old and so it the furniture. I think it looks just fine and the person who decotated them did a good job. The master bedroom has its own bathroom ; for the other rooms, you'll share a bathroom, which I've always seen extremely clean. And it has a huge shower cubicle with a double shower head, which is definitely a nice touch.
And now for the best part : It's just like staying at one of your relatives! Walter, the owner, is a really sweet gentleman, very knowledgeable about stuff to do in the city, places to go, restaurants, hikes (he recommended a few hikes that I adored). He loves to discuss everything over coffee in the breakfast parlor. You can talk about politics, San Francisco...anything, he's a very interesting person to talk to. Also, i you aren't a chatty person he's not intrusive at all. He will introduce you to the other guests, who during my stays were also very interesting people. Breakfast is one of my favorite moments there. As a woman traveling alone, what could be lovelier than having your morning coffee chatting with a few charming and funny gentlemen? The atmosphere is friendly without being too much. I easily feel overwhelmed by people but that was never the case there. Also, I should mention that Walter's staff is also very friendly.
Breakfast is good. I saw some people on Tripasvisor didn't like the fact that there wasn't a real kitchen. I think the parlor room is a very nice place to have your coffee, juice, cereal and bagels. Walter even brings in the morning papers!
And to finish with, the fact that it's a gay (and very straight-friendly) guesthouse is also an important point : to my mind, it's importat that places like 24 Henry continue to exist, for the identity of the Castro and SF, but also to provide a welcoming place for gay (and straight) travellers).
To summerize it all : just go!

I had looked forward to the more personal experience when booking into 24 Henry from the reviews here on the site. I never experienced them. The place is dated, the decor are old, and the utilities from another age altogether. Breakfast is a couple of bagels placed in a cupboard in the living room. And so on. But location is good...

My partner and I stayed at 24 Henry this summer, opting for the master bedroom so we could have a private bath. The location is excellent, if you want to be in the Castro. Very easy to walk everywhere you need to.

I can only echo all the kind things that have been said about Walter.

Perhaps most useful would be to compare it to Inn on Castro which is just a couple blocks away, where we stayed just a year ago. In comparison, 24 Henry is an older property and has had more wear and tear. It's tastefully decorated and clean, but the door knobs are getting loose, and it just feels a bit old. Having said that we felt very comfortable there. Inn on Castro was newer, breakfast was better, but the management treated us indifferently on the best days and rudely on the worst days. Inn on Castro is also a bit pricier.

You get what you pay for, and when it comes to customer service, 24 Henry definitely gave us better vibes than Inn on Castro.

Recently spent a week at 24 Henry and we were very happy with the accommodations and reception. We needed to change rooms two times during the week because we had waited until fairly late to book and there wasn't a single room that was available for the full week, but this was not a problem. The house is on a pleasant, quiet street, near Castro but just far enough away from the bars so nice and quiet for sleeping, and we felt safe walking home at night from the MUNI and streetcar stops. Walter, the owner, and his co-workers were very friendly and talkative with guests, helpful with suggestions and directions. We spent the first night in the room that has its own bathroom and shower and the rest of the stay in rooms that had to use the washroom in the hall, but this was never a problem. This place has a cozy, welcoming character rather than looking like something chichi from a home-decor magazine, but the beds were fine and when you're out all day seeing the sights, all you need is a comfy, quiet place to sleep. The rates are also very reasonable compared with what we found at hotels and several other bed and breakfasts, so you can't expect the Fairmont.
A light breakfast (cereal, toast, muffins, coffee) is included each morning as well for those who would like to save even more money. You serve yourself and have to sit at a couch in the living room, since a table is not available. We preferred something more substantial to start our days so we usually ate breakfast at the Squat and Gobble nearby, a friendly place near Cafe Noe that serves nice omelettes and fruit, crepes, waffles, etc...
Walter has also generously included two computers in the living room for guests' use, which we found helpful for looking up sites, restaurants, etc. and he has many books and magazines on the area.
When we reserved he gave very clear, precise instructions on how to get there from the airport..easy to go on the BART train and then transfer to MUNI at Civic Center station.
There is a very nice French bistro, called L'Ardoise, just up the hill from the guest house, at Henry and Noe...which seems to be very popular..Had a delicious tarte tatin there for dessert one night, though we didn't have dinner there.
We left SF very happy with our accommodations choice and the great sleeps that we had each night. For one thing, the nice cool breeze at night in June made it great for sleeping compared to the often muggy hot nights on the east coast at this time of year!
I'd happily recommend this to others as long as you recognize not to expect four stars, but you do get a warm and friendly welcome from Walter. Thanks, Walter!