How does mandatory migration control - not the fault of an airport - make an airport bad? The design of the airport is the bigger issue.
Anyway, whereas I'm no fan of JFK - nor any of its terminals - I think ICN is also overrated. There's no space to gather your belongings after passing through security, the miasma from smoking rooms too easily wanders into the immediate area, and signage at the train station isn't too clear. Food options are also ho-hum.