shamus... only level 40? and a hunter?
oh well, you apparently have better things to do.
You made a decent list of the things that WoW does right, but you missed a big one (probably because you reached level 40), but Raiding is a huge part of why WoW works. When they do something right, it clicks, and is wonderful. The feeling of accomplishment in first completing a raid is unlike anything in the world of gaming. It used to be a luxury thing, getting into a raid group, back in the early days of WoW, but it's a common thing at high level play these days to get into a raid. Raiding is an accessible, and still challenging gameplay device that is pivotal to WoW's success.
Also, Wow's complete embrace of the Achievement system has lead to another layer of "things to do". Sure, you could always kill Booty Bay goblins to get your red pirate's hat... but now, you get an achievement, and the title Bloodsail Admiral. More people might consider doing that for the title, and the achievement points, then those who thought before that making the goblins hate your guts wasn't worth a red pirate hat. Add achievements to raids, and World First achievements, and you have yourself an addictive spiral of success and Win.
Like someone above said though, if a game were to try to do everything that WoW does, but better, they will ultimately fail. It's best for them to try something new, take some queues from WoW, but try to innovate. They'll probably fail at that too, and in the end, if it's good, WoW will steal it, but you might find enough success to make it worth your while.
Another thing to do is go an entirely different route - changing the setting of a WoW clone can entirely change the game, and make success a possibility. Having it based in the real world, or in a futuristic setting, or something even crazier will work better then another fantasy roleplaying game - you can't beat WoW at the MMO race with a fantasy RPG. Not right now.