I could jump on the hate train and say DHs are overly op in every imaginable way - like having insane AoE while healing themselves, dealing insane amounts of damage and unlimited draw while playing 4 1-drops in the first two turns. I am not doing that though. 
I want to talk about its class design and how it feels to play against them.
Playing against a DH is never ever fun. It always feels like an uphill battle.
In the majority of these games while facing a DH you’ll be on the passive side and all you are doing is reacting to the DHs plays.
Being constantly on the passive side is not fun - especially while playing a supposed to be tempo deck yourself.
The fact alone, that DHs have a 1-mana hero-power is utterly stupid. There is no other class that always has a guaranteed turn 1 and is always able to utilize all of its mana in the most efficiant way just through their hero power alone. Imo this is a critical design flaw and needs to be fixed.
Even winning against a DH never feels rewarding somehow. Mostly you win because you found an answer to all their plays and they do run out of stuff eventually. You don’t win because of superior plays or good strategy - mostly you win because they concede - so u win without being on the active side of the battle once - it is just not fun. The whole class design is a failure, especially when blizzard is slow to fix its current state. Since DHs have been in the game, expansion launches have been worse with unnumbered DHs torturing the ladder and souring the usual fun a new expansion brings…
