I don't get why you're all like "play with friends" the game is more solo friendly now then ever, I played through both pre cata and cata completely by myself (apart from being plvl'd about 5 levels) and cata world is fun solo too (Apart from the night elf starting area. That place still sucks quest wise.)
I think the main reason i stopped playing (apart from rift) was, I loved warlock but once they changed how soul shards worked my brain couldn't comprehend, And then i turned into a healer.