I have always played games for the lore. Always. I played Warcraft III, and it's expansion The Frozen Throne, and the lore in those games was great, if a bit bloated by the time the expansion came about.
Then you had WoW come along, and in shrinking the scale of the player, they utterly destroyed their lore. The scope of the lore increased to cover every single speck of dust on both continents, and I found the world a lot less interesting when a newly created orc warlock had to walk all the way to Orgrimmar to deliver the Great McGuffin to Thrall, or something similar.
Which brings me to my next point: the stories were less interesting. There was no personal motivation for your character's actions in quests. Everything you were doing was at the behest of some person you barely knew. I suppose this is an innate flaw of MMOs, though; there's no character development. You play the same damn person through eighty or so levels: a person easily replaced by a flat cardboard cutout.
Finally, there's the incredible(and i mean incredible) plot discrepancies introduced by the expansions. Which was it, Burning Crusade? Introduced the blood elves on the side of the HORDE. With the UNDEAD, and the ORCS, who their people had been fighting for *centuries*. Against their recently broken-up allies, the humans, dwarves, etc. The Draenei somehow find a *spaceship* and smash it into Azeroth, somehow losing their strange carapaces and becoming beautiful blue space aliens with glowing eyes that bear a striking resemblance to night elves. (
http://www.youtube.com/watch?v=XDQPVFCR1m8 Check 0:00 to 0:40. The first guy that speaks is a Draenei.) Oh. Just looked it up. Apparently they had to make a massive retcon just to explain why the Draenei look different, saying that fel energies from Outland mutated them - despite them having originated from Outland in the first place! Wrath of the Lich King made it cool for /everyone/ to become a death knight! Whopee! Cataclysm added a race supposedly from a 'legendary kingdom'- one I've certainly never heard of before! Never seen a Worgen in any of the Warcraft games, as if their lore wasn't bloated enough. And then Mists of Pandaria. My god. They took the Pandaren, which were entirely a *joke*- no, really! The only Pandaren that ever showed up in either WCIII game were as a joke reward for beating the secret bonus level of the 'human' campaign of WCIII:TFT, and then they were hireable in multiplayer maps from the Tavern building. And they made these guys into a serious, full-fledged race. Not to mention adding an entire new continent for them.