I used to play games every free minute I had when I was younger. I passed up so many social opportunities in both primary and high school because I'd rather stay home and play video games. I was even so renowned in one game community that the company even contacted me to play an early demo of one of their releases and post a review of it online.
Nowadays I'm a much more casual gamer. I only play a select few games, but those few games I do play I'm utterly obsessed with. However, I value other aspects of life a lot more now - I'd rather go out for dinner or a drink than stay in and play by myself. "It's just a game" after all...
I prefer single player games. In fact, AC:NL is the only game I play with an online feature.
i can really echo Tina's first paragraph here. i'd chose games over other people at every opportunity, but i was surrounded by cousins and siblings who loved games, too, so it wasn't such a solitary childhood, although i wold game for much longer than any of my famiyl members.
once i got older, i still played a lot, but real life responsibilities would often get in the way. i still played a lot, though, and never thought i'd grow out of it. i still play now, but i'm about to go to college, so i suppose my priorities may change.
i also prefer single player games, but i have gotten over some fears of playing with other people by playing TERA and other mmorpgs and, of course, acnl.

i think the downsides of playing with other people will always be there, but when you find decent, good people to play with, it pays off to play with others. however, i do like the comfort of "offline" single player games. i like a complete, condensed story instead of one that always has add-ons or whatnot.