I've never been a fan of multiplayer games, because really, I want to interact with a guided vision, not my pals from the internet. ... Say what you will about the BioShock "choice," for example, but we're all learning from the differences in one another's experiences of the same event. Meanwhile, the story of your WoW raid is solely personal, and interesting only to you and your guild.I tend to disagree with this opinion. Not so much that multiplayer games like WoW and L4D are better than singleplayer fare like Bioshock, but more that each has it's own place. I enjoy playing titles such as the Final Fantasy and God of War series. Yet I wouldn't be able to stand it if I had to play a 40+ hour scripted game with someone else because I would want to experience it in my own way and at my own pace. By the same token, the thought of joining an empty TF2 server by myself and running around on my own just depresses me.
This is almost heading into the 'games as art' realm, but I think game designers would do well to remember that most people still buy their products because they desire a game to be entertaining. And for many people, the social interaction of multipayer games is what makes them entertaining.
Not that I think we're in danger of losing either subset, but it's important to remember that both are necessary as each one fills a role that the other cannot. A well-written and properly executed singleplayer game, like a good book or movie, can create an emotional investment with the characters or may even give a new insight into something that had never been considered before. However, there are few things more entertaining than getting together with friends and splattering the heads of a horde of zombies.