LOL Mage decks are some of the MOST expensive decks out there. Oh the QQ on this thread is legendary! hahahahahahahahaha
Actually, the problem is that since we've been playing for months, a lot of people have those big expensive cards. So, the late-game, super expensive mage cards are now becoming a huge problem after Blizzard nerfed every single counter people were using against that kind of mage late-game deck.
This this and more of this. Right now unless you're a Hunter and happen to have the only Flare in your deck (because running two is wasteful) in your hand on the exact turn that you can pump out enough damage to kill him (which you *need* to do that turn, because next turn he'll kill you regardless of what you do), if the Mage has the right cards there is nothing you can do to win.
The only way to beat a properly-constructed Mage deck is for the Mage to be unlucky. That is *it*. You can't outplay Ice Block (see above), you can't outplay Alextrasa (which may as well be a Mage staple card), you can't outplay Pyroblast or the Fireball+Frostbolt+Ice Lance combo, unless you are also a Mage
because, hey, let's give the only anti-spell mechanic to the spell-specialist class!
It wasn't as bad before solely because there were other OP decks that could deal with it. Priest controls dealt with Giants and such with ease, Rogue aggros could overwhelm before the lategame came, Hunter OTK could ignore the Ice Block and get the UTH combo off before turn nine, but all that is gone now. Nothing can defeat a properly-built Mage now other than really bad draws, another Mage or a ridiculously lucky Hunter.
Mages needed to be nerfed in the last patch and the one before. Until the next patch the meta will be Mage (or, sometimes, aggro or Giant Warlock) or bust.