I think ep4 was the shortest after ep1. It only took me 3-4 hours to complete it while ep3 took me days. The puzzles were easy to figure out, no long conversations with any character (almost no conversations at all). The only long thing I can think is the fact that you had to go back and forth to the islands to get stuff you needed to go on with the game.
I really love this game, I played all of KQ tons of times and I'm very happy that someone made this perfect game after all this time.