The story has always taken itself fairly seriously even in WoW (for the most part). The game, however, never really has. The easiest thing to point to is the script from clicking on the units in the RTS games, which goes back to Warcraft 2 for sure. Warcraft: Orcs & Humans I can't recall for sure... Also, clicking on critters until they explode (yeah, that's an easter egg but still). Certainly, WoW takes it to a new level but I think that is because Blizzard has made it more a part of their identity in all their games and WoW just has loads upon loads of content to put stuff like that into.