I have stayed at the other holiday inn express at Seoul Euljiro quite few times and have never been disappointed.
Official website here:
https://www.ihg.com/holidayinnexpres...x/hoteldetail?
Good rates, friendly staff, decent size rooms and bathrooms, nice breakfast selection (for a HI express anyway) and useful central location with metro station nearby (2 lines passing through). This one also goes for 20,000 points for a free night.
Hopefully this new one will be up to the same standards as the Euljiro property.