I only stayed at Anteroom for one night, but it was perfect for a base if you're not spending much time in the hotel room and preferably have things on the agenda in Gangnam, Hannam and Seongsu-dong which are all fairly quickly accessible via bus or taxi. You can also get up to Anguk and the Palaces super easy via the metro which is close-by.
The rooms were fairly small, but cozy and comfortable with a good layout. The rooftop bar has an amazing view, beware of it closing quite early tough (last order a solid while before that as well) - so I missed out on sitting gazing over the Han River, Namsan Tower and this vibrant city up there unfortunately as I only stayed the night...
Overall I had a good stay at this hotel and would consider it again.