More than the botched LOST ending and unanswered questions, what really got me was how they took Locke from a "special" person early in the show, that was healed by the island, in touch with it, a hunter, a skilled guy that found his place on the island after being basically a loser back in the real world that constantly got taken advantage of and shytted on.
He was such a strong character and then I don't know if it was in the grand scheme or not, but after his body was in the casket and they made him out to just be a loser that wasn't special after all, even on the island, they really threw his character in the bushes.
Still, props to terry O'Quinn for being able to play a loser Locke, awesome Locke, and the Man In Black. He took the bullshyt the writers started giving him latr on in stride and made the most of it.