Slimebeast on 04 April 2013
Single player rules but so does online.
I have had so many thousands of hours of fun online - with online shooters like ET: Quake Wars and Battlefield, RTS games like Age of Empires II, with RPGs like Dark Souls and Two Worlds II, and even with MMORPGs (Dark Age of Camelot back in the day was amazing).
Like the OP says, there's so much with multiplayer that is unique:
the adrenaline rush, the competition and pride, the dynamic gameplay with surprises and creativity, the competition and true challenge, the superior human AI, the social aspects like teamwork, friendship and the feeling of being a part of something bigger.
