for a long time I only played single-player games and despised anything multi-player. I could enjoy a game of hot-seat HoMM or something along those lines, but that was it. these days I still prefer single-player, but do play a lot of multi-player games as well. I play League of Legends regularly and I've played my fair share of MMORPG's. I can only take so much before I grow sick of idiots and people who think playing on the internet gives them a right to be assholes, but once in a while it can be really fun. especially with friends.
the problem, however, is that the two get mixed up way too often. for me there are single-player games, and there are multi-player games. two completely different things, and that's the way I want them. but too often developers seem to think they can mix the two together and create some kind of glorious hybrid. it HAS worked on rare occasions, but only for first-person shooters as far as I know. but even then, if I enjoyed the single-player mode I don't bother with multi-player. the way I see it, one always takes away from the other. look at the Call of Duty games - I can admittedly enjoy the single-player campaigns when I'm in the mood, but they've become worse with every new release (CoD 2 was the best one). less inspired, less story-driven and shorter. and this is no doubt because the developers put more focus on multi-player, and only include single-player "just because". why don't they just drop the SP mode already? no one seems to play it these days anyway. and if they want to make a cinematic first-person shooter, let it be an off-shoot from the regular series with all attention focused on story?
then we have games like Dungeon Siege 3. I've played through half or so alone, but I just keep thinking that this is a game that is supposed to be played with at least one more person. but the only thing I hear from people who've played it in co-op is how badly it works. and this game tries hard to be an "rpg", with lengthy dialogues and a lot of lore to read up on - no one wants that in a multi-player game, there's always someone who can't be bothered with it and will grow bored.
lastly, we have Mass Effect 3. the MP component might sound like a fresh idea and could be fun, but it will only be fun until most people have finished the main game and moved on. after a year, or maybe even less, the number of players available will have dwindled and then what about all those resources the developers put into that part? this, too, is a very common problem. the multi-player aspects of a mainly single-player game rarely live long past release-date these days. and yet developers spend time and money on half-assed multi-player modes. I really don't understand why.