I did not meet any staff in the facility but I have been communicating with one online. They answered all my questions regarding very late check-in. They sent me pdf files of how to get to the hotel coming from the train station on foot and access code to enter the building and instructions on how to check into my room.
My unit was very pleasant, clean and welcoming with a dinning hall, sink, appliances for use during quick meals. My room as well was clean, well lit, presentable and comfy. The bathroom is big with high quality toiletries provided.
The double bed was firm yet comfy to sleep on.
The AC worked so well that I felt cool all night long.
Breakfast was just the regular: cereal, milk, toast, butter, strawberry jam and coffee and tea.
I really liked staying in Incheon Airport Guesthouse L. I will book it again the next time I visit Seoul.