I usually play single player games these days, but that's because of a crappy computer and crappy internet.
There is certainly a place for single player games, and most games I don't touch the multiplayer component, but there are some where multiplayer really makes it happen.
The most fun online I've had was with IL2-1946, plus teamspeak, on realistic servers. Flying with real people, against other real people, blew single player out of the skies. This was mostly due to Teamspeak, I think - talking directly to the people you're flying with makes it a real multiplayer game, rather than playing against a silent faceless thing with a funny name.