Having worked in Incheon, ISTR there is a memorial site there marking the landing, as well as statues of MacArthur etc. You can get to Incheon city by subway from Seoul. It's not the most exciting place apart from that (the airport is on an island off-shore).
My impression was from being there that the nations which assisted Korea during the Korean war are still viewed with much gratitude by the Korean people. I was there during a memorial, and newspaper reports listed out all countries (and there were way more than I knew) who sent troops to assist Korea during the war.