If you are looking mostly for a place to sleep, this is a good option. It is really serviced apartments, and does not offer other hotel services. The biggest plus? It was quiet. There was a bit of airplane noise, but less than I would have thought, and there was no noise inside.
The room is a small apartment, with basic furnishing. My room had a large living area with a kitchenette, small bedroom, small bathroom including washing machine, and a nice terrace. It would be great for someone who needed to be in the airport area for a longer stay, but is much to far from Seoul to consider for people visiting the city. For most it will be a bit excessive.
Included were handtowels, shampoo and conditioner, soap (large bar already open), toothpaste (large tube, already open). The room and sheets were clean. The bed is firm, but I wouldn't say hard. Comfortable to me, but those picky about beds might not be satisfied. Wifi was good, but unsecured. The heat was good and the controls easy to use.
There is a minimart on the first floor, several restaurants, and even more restaurants nearby. There is also an EMart, which is a huge discount merchandiser just up the street.
I was a little concerned about an 11PM arrival, but went to the airport info desk, which dialed the number and connected to the guest house. It was a little hard to hear, but got the directions to go to the 3rd level (arrivals) gate 5 (I think) to get the shuttle. Two other couples took the same shuttle. The shuttle is a small, unmarked van. We arrived, went to the 8th floor for a quick check in, and to our room. No need to check out--just leave key in room and depart by noon. The English on the phone and of the shuttle driver/reception were fine.
There are shuttles back to the airport, but there is also a frequent free airport shuttle across the street, and directions in the room.
It might seem a bit odd to arrive here alone late at night if you are not used to staying in this sort of guest house, but it was quite good.