my main issues with JFK are the way it's so spread out and if you are transferring between terminals it's a total PITA. You walk a mile, then go up and down a bunch of escalators. Hope that the Airtrain is actually working. If not you might have to take the train away from the airport and change to one going back to the airport. The layout just isn't very efficient. Some of the terminals are not very nice places to spend any time. Low ceilings, cramped gate areas. Surly security staff.
I will encounter ICN for the first time next week so I am looking forward to seeing if it lives up to the hype.