One major difference between the goals of the Korean War and the goals of WWII was that the goals in WWII were much clearer. In the Korean War, it was not always clear what the goals were.
In WWII, the Allies had stated from early on that the goal of the war was to force the unconditional surrender of the Axis. This was a very clear goal. By contrast, it was not clear as to what the Korean War was for. Was the goal simply to push North Korea out of the South and return things to the status quo ante? Was the goal to overthrow the communist regime in North Korea? Was the goal even to extend to causing a war with China as some hoped? This was not at all clear and it led, one might argue, to the conflict between Pres. Truman and Gen. MacArthur that ended up with MacArthur being relieved of duty.
On a more detailed level, the goal of the Korean War, one way or the other, was to oppose communism. This is as opposed to the goal of WWII, which was to oppose fascism/military aggression.