I stayed at Hotel Crescendo for 2 weeks and had an amazing time. Although my room was a bit small by western hotel standards, it was very comfortable, clean and well maintained. The hotel has a restaurant downstairs which offers options for breakfast (4 options - granola and yogurt, omelette and sausage, beef porridge or brioche toast), as well as lunches and dinners. Conveniently, there’s a McDonalds next door and plenty of other cafes and restaurants within a short walking distance. There is also a subway station within a 4 minute walk from the hotel.
The staff are very nice and do their best to accommodate your needs.
I would recommend hotel crescendo to anyone visiting Seoul.