He was inconsistent but honestly wasn't terrible until he signed his contract. I mean, there were enough signs to not sign him to such a deal, so this one is definitely around Blake's neck, but he had a good showing at the World Championship and did play decently with the Kings before. He had some leverage in negotiations and the Kings were willing to bet on at least giving him three years to see he could take the spot, but he has just been a complete disaster since.
In the end, the immense pressure to take over for Quick and be the bonafide #1 of the team just mentally obliterated him. There really is no other reason or description for his performance. He hasn't been good at all, but you can literally see the mental devastation in his eyes when he is out on the ice. He looks like a guy that doesn't believe he could stop anything and wills it into existence. He has the physical attributes and the capability of being a decent goaltender, but I don't think there is any way to save his mental state at the moment. Maybe something happens in the minors that helps him find his way back, but I think his mind is toast.
He is a weird case in that he has all the tools, but is the most visibly defeated goaltender I've ever seen.