Blizzard's biggest enemy is: World of Warcraft
Yes, sounds funny at first but it is.
Like it or not, with WoW Blizzard has overrun the MMO market and rules since back then. Does it anything brand new? No, it copies from all sides, but it copies good and that works.
But what now? Sure it is one of the most sold PC games and the subscribers still there are making Bliz a lot of money.
Looking at the MMO market i see some nice games coming up, but none really challenging WoW as #1.
GW2 is b2p so why cancel your WoW sub? you can keep both.
And SW:ToR (my personal messiah ^^) is just to big a name to satisfy everybodies imagination one has about Star Wars. It will be big, it will have lovers or haters, but it will not challenge WoW anytime soon.
Blizzard now comes with Diablo 3 but it is just something different so it will not be a "WoW or Diablo 3" choice for the players.
Also Blizzard has allways the RTS Genre in the backhand where they are really good at.
But the MMOs? If they want to stay on top in that market now their task is to exactly hit the time when to pull some of their chief devellopers out of WoW into a new game that can again be "opium for the people".
If they wait till their subscribers go down it will be too late to start develloping a new game, right now it would probably be to soon.
So i guess the most valuable job at Blizzard the next few years will be market trend analysts.
Disclaimer: it is all my personal opinion. you don't agree? that's ok..but then discuss, don't flame :)