Carl's house is unique: you step into what seems a Victorian explorer's home in the middle of one of DC's most rapidly developing, and storied, neighborhoods. His library is really a treat for the bibliophile, and while I was there on business and hadn't the time, I did flip through some books I now know I want. He's a DC native and very knowledgeable about the city too, so you'll leave knowing more about where the city came from and where it's going than on your average trip.
The house, as the description warns, is indeed a work-in-progress and might not be the right cup of tea for the very cleanly. But the room itself is perfectly fine, decked out in Balinese and Javanese art. The bed is fine, but not for those who prefer a soft mattress (it's quite hard, which I prefer). You can do your laundry and cook, which is great. Wifi is a bit slow, especially on the second floor.
Overall I'd say Carl's place offers an Airbnb experience as it should be: unique in character, shared with the owner, and placed at a city's beating heart. It's not the 'private hotel' experience many have come to expect, but that's a good thing.