I visited this restaurant 3 times when I travelled to Seoul couple of weeks ago. It's on a small side street of very popular Insadong street. It's not really a Loving Hut -restaurant, but it is connected to the same ideology. They also sell vegan food products in their small shop.
Food was good. Even though all the food is not Korean, you can experience the Korean way of eating with all the different side dishes (always including kimchi) served with any main dish you order. Also tea is served for free. They have both very spicy and some quite bland dishes.
Service is really nice and friendly. And I found my Lonely Planet -book there well guarded the next day after I forgot it in the restaurant.
You sit on the floor, so you have to leave your shoes on a shelf when entering the restaurant.Pros: Good food and service, Vegan, Central location