If I was going to pick on a game design thing that I look back on and think was a mistake? We really never designed WoW to be a competitive e-sports game; it was something that we decided to start tackling because there was such a desire and demand to evolve it in that direction, to introduce competitive arenas. I'm not sure that that was the right thing to do with the game.
We didn't engineer the game and classes and balance around it, we just added it on, so it continues to be very difficult to balance. Is WoW a PvE cooperative game, or a competitive PvP game? There's constant pressure on the class balance team, there's pressure on the game itself, and a lot of times players who don't PvP don't understand why their classes are changing. I don't think we ever foresaw how much tuning and tweaking we'd have to do to balance it in that direction. Either I'd go back in time to before WoW ever shipped and change the rules to make the basic game more conductive for being an e-sport, or if not that, just say it doesn't make sense. Right now, WoW has a bit of a schizophrenic philosophy behind it, and we're trying to figure out how to guide it.
It's tricky, now that we've gone down that road, because we have a passionate, large audience that enjoys it - the Arena, the e-sport - so we can't just chop off that head. We can't just say, "We fouled up and will go back to how it used to be before," because we have a really passionate audience that wants it in the game.
If I could go back in time before we shipped WoW, I would have either made serious changes to basic class balance to facilitate that type of play, or if I went back to when we had the idea two years later, I would have said, "Maybe we shouldn't go there."
) but it's a little difficult to level up I guess (I can't say but that's something I've been told). If you lmanage to go level 80, it will be great, there is a lot of demands for tanks in groups 
