So, let's talk about decks we're glad exist if only so they counter specific archetypes that should exist but must be kept in check.
What just made me think of this is how Freeze Mage is incredibly strong against midrange decks that focus on flooding the board with sticky minions. Zoo was an example of that, but now totem shaman and this new Murloc Paladin would qualify as well. Freeze Mage may be annoying to you, but its existence helps keep the power of these types of decks in check.
Patron Warrior is a strong counter to all types of token decks, be it Druid token or face paladin (not necessarily tokens, but crappy minions as well) or totem shaman.
Any other decks which provide an important hard counter to specific archetypes or styles?