If I could, I would definitely give this guesthouse more than 5 stars; it was one of the highlights of my trip to Korea. The couple who run Owl Guesthouse are extremely nice and helpful. They both speak English (as well as Mandarin and Japanese) and went above and beyond to ensure I had a good trip, giving me recommendations on the best places to visit, find information about special events, and how to get around not only in Seoul, but also in other Korean cities. They even invited me to join them for dinner. They also let me check in early and store my luggage for a day after I checked out.
As for the property itself, it is very clean, comfortable, and safe. It opened within the last couple years, so the rooms are very new and in great condition. The rooms have air conditioning, and also a new keypad lock system that makes you feel quite safe and is also more convenient than carrying around a key. They provide a free breakfast, common area to eat in, as well as towels/shampoo, and even TMoney transportation cards.
It is located between two subway stops on line 1 and 6(5 min walk away), and a major bus station, and it doesn't take very long to get to Seoul station or other main attractions (such as all the palaces) by subway. There are also a number of good restaurants and coffee shops nearby.
Overall, this guesthouse is a great place to stay, and provides service of a level well beyond what you'd expect for the price. I'll definitely stay here next time I'm in Seoul.