Alea, I know all about the game. 1.5 million is only for North America. Though you're right--5 million isn't right. I forget where that number comes from; I think it might have something to do with the character numbers, possibly. But either way, 1.5 million in North America DESTROYS all other Susbcription games by a large margin. I'll keep myself safe from now on and say "Millions."
For the amount of players in the game, occasional lagginess due to en masse playerbase aside, I'm amazed at some of the technology employed. On my machine the game loads an entire continent in under 10 seconds, and NEVER has to load except for maybe a 5 second interval when I enter an instance.
I'm sorry for the inadequacy of my statements on the numbers (Though I'm sure if you add WoW Europe, WoW Korea, and WoW Eastern Asia, they are more than double the North American figure). What I have to stand by on is the player models; I have yet to see two people looking even remotely similar outside of certain inevitable pieces of armor or weapons (Valor Shoulders, Whirlwind axe, Green Iron Hauberk). Even then, those pieces become milestones for players--it's like, "Hey, awesome, you got the Aegis of the Scarlet Commander, welcome to lv35-40!"
Also, many of the weapons models are similar but every patch more and more of them are updated; many of them are "placeholder" models and on each of the three major patches many people have found themselves with new models for some of the more common equipment.
I wouldn't worry much about the lag. If the Alliance zerging were kept to a minimum like most of us horde wish it would be, the servers on the whole would experience a lot less of the raid lag problems, I wager.
Either way we're caught up in discussing the game and not answering the question. And to answer the question I would easily say WoW is the best MMORPG on the market today. And I say that in good confidence.