Stayed at the Ibis in Gangnam for 2 nights in June. Had the non-smoking double bed. My thoughts:
1) Really clean room! The cleanest I have seen during my 2 weeks in Japan and Korea.
2) Free internet! Can't be beat and it is high speed! Only LAN though
3) Very helpful staff but don't expect a concierge or a bellhop.
4) Free internet in the business centre
5) Good location, 10 minute walk to Samseung station in the COEX mall. COEX has great shopping. Gangnam area has lots of shops and restaurants to check out. My only gripe is that if you want to go north of the river, to Myeongdong or Dundaemoon or Hondae, it is an hour subway ride one way. If you are planning on staying south of the river, this place is amazing.