As what I'm understanding through some form of consensus is that multiplayer does in fact enhance replay-ability, interest, and many other things. Personally, "good" multiplayer does factor-in and influence whether a person may or may not purchase that game and enjoy it, its understandable. However, I do find that it does present some negative sides as well - unless, the game manages balance single/multiplayer respectably (very rarely though).
What it seems to me is that the main focus for mainstream video game developers is to enable people to connect in social groups and connect to some form of community. However, this focus does leave several aspecets of a video game behind. Both artistic and immersive dimensions of the game eventually diminishes to a point where "its just a game to play with friends" or "its just a game to get 'x' amounts of rewards and brag about it to other people online and to your friends". Moreover, this focus in multiplayer does lead developers to neglect its roots as a video game. Sure, video games are supposed to be fun, and essentially gameplay plays a large role in its successfullness, but sometimes it just feels like "another game". What really makes games different and memorable is the feelings we get when we truly feel immersed into another reality; immersed into something that pulls on our creative psyche.
Take, for example, Mass Effect. Mass Effect conveys a very detailed and creative universe that makes us (or some) want to believe that it was true. We become engaged to the many conflicts within the universe and begin to realize that we are truly apart of the game. Maybe I'm overexaggerating some apects of it; but understandibly, it's a lot more immersive than many "other" games. The story of the game or the universe of the game can ulimately generate more interest into that game.
What really irritates me, however, is the amounts of assumptions that many developers make. Quite often, it is insinuated that about 90% of the video game community are numb-skulled and can't read a book properly (this is untrue). It seems like the bad side of the gaming community is brought upon multiplayer-focused games, like for example: Call of Duty, Halo, and WoW. Yet, by no means should future video games be like this and become another part of the so-called-mainstreamed video game collection; it just doesn't present much evidence that video games will eventually evolve. More likely than so, it just stunts the growth of video games. Because of this, it creates the lack of interest into the perspective of story, plot, etc. Yeah sure, if you want to be engaged into story or plot, read a book. But why does that mean that video games can't be another source of plot development? Personally, video games have the potential to be far more immersive than a book, or even a movie; the interactions of an individual to virtual reality greatly enhances the immersiveness of the story development.
Finally, I find that game developers are running out of ideas to make a good game. Ultimately, they are just forced to focus on multiplayer and seem to tag along other successful games in hopes that people may play it. More specifically, and most importantly, is that video games aren't getting original anymore. It seems like that almost every game that is being realeased seems to be a copy of "this" and a copy of "that". When everyone starts to copy and take ideas from other games, this really leaves little to no room for expansion in actual "good" games. More than often we find many games that are WAY to alike. Honestly, is this what the gaming industry has become? Is it just the same game over and over again with just a different look and feel? Come on, really?
What I'm ultimately saying is this: multiplayer is fine, but it better not be the same game I played a couple weeks ago - and I better have a damn good game to play if my connection isn't working!.