I feel like the achievement system is very anti-new player. As a newb I want to focus on building one class that I know solidly before moving on, but to get any $$$ I have to be hopping from class to class from the get go. Preventing me from really learning any of them.
Stupid....
In time, you'll realize that this is the best way to learn about the game because there is nothing more educational in card games than to play as and against any given deck/archetype, because only then can you truly appreciate the problem from both sides of the table. Think of this less as impeding your ability to learn a single class and more about exposing you to the game as a whole.
And the time you spend on these initial quests will be a pittance compared how long you'll be playing Hearthstone, assuming you're a typical Hearthstone player.