Been to ICN, PEK, YVR & SIN (although my last time through SIN was about 8 years ago now). Obviously haven't been to HGK to compare, but ICN is definitely a class above all the other airports I've been to (e.g. MEL, DUB, FRA, LHR, PVG, SHA, SFO, BKK et al). Some of the other airports might be somewhat controversial entries to the list, but having been to ICN, I can see why it's always at the very least on the podium, if not walking away with the gold itself, in these rankings.
Bit unsure about YVR. It's certainly a nice looking modern facility, but there are some seriously long walks to some of the international gates, such as the one I had to trek to to board my AC flight to PEK. At least they have largely put the duty free shops to the sides unlike using them to form an obstacle course à la MEL. PEK is a bit similar to YVR. The subway link does work very well though. Will be interested to see how the Beijing Daxing airport turns out when it's finished.