I consider myself a core gamer (I've bought about 50-60 over this gen over several current gen platforms) but I do very little online gaming. I spent about 15 hours on COD:MW1&2, another 15-20 hours on KZ2 and maybe 10 hours spread across a plethora of games. With COD and KZ2, all that online time falls with 3 2-week periods.
I consider online gaming very monotonous even though I use to love military based FPSes on PC where over time I enjoyed going from max 32 to 64 to 150 on Joint Ops:Typhoon Rising with super huge maps. I kind of fell off with online gaming after Battlefield 2 on the PC when I migrated mostly over to console. My desire to online game never really migrated over with me.
Maybe its the concept of going from single player to multiplayer that bothers me, as it only highlights the act of going over the same handful of favorite maps doing the same thing over and over again. In my view the concept hasn't really changed all that much over the years.
I'm inclined to say that I'm tired of games trying to cover both single and multiplayer fronts. While I understand developers trying to keep their games relevant and "long lasting" by having multiplayer, it's true that so many of these games just recycle single player maps. However, some like CoD and Rainbow Six Vegas do a good job keeping it fun across both modes. I just wish games like Uncharted or Mafia II which are completely story driven so much from the get go would stay single player, offering a longer campaign, or co-op campaign/side story/whatever in place of versus multiplayer. That to me would be exciting, though unlikely, since the length both Uncharteds' is just about perfect in length and pace (so I would be all for dedicated co-op campaign or likewise DLC). It surprises me that Mass Effect has stayed single player, though co-op would be cool, but would mean changing the structure of the game. Mass Effect at least fulfills my need for a long game, and has plenty of replay value.
BF3 I could care less about single player, but I may invest in it once it hits if it looks compelling enough. Right now, I don't give a flying fudge.