The Dark Knight
Batman Begins was one of the best films I'd seen, and I loved Christopher Nolan's other films, particularly The Prestige, Memento and Following. The Dark Knight was receiving rave reviews, and the death of Heath Ledger added even more fervour - the best villain ever and that sort of thing.
So I went to the cinema to see The Dark Knight with huge expectations. I'd loved the darker tone of Batman Begins, but The Dark Knight went too far. I found it boring, drab and depressing, with a lack of soul. I didn't care what happened and was barely entertained. The best think about it probably was Heath Ledger's Joker, which was good.
As a result, I haven't watched The Dark Knight Rises. As for Christopher Nolan's films since - Inception was good, Dunkirk was okay, and I haven't seen Man of Steel. Those earlier films were his finest hour.
At least I've learnt to go to the cinema without any expectations, positive or negative. I ignore reviews until I've seen the film for myself.
My new favourite director I have high hopes for is Duncan Jones.
Another failure was
2046, which had great reviews and looked like a cool sci-fi. It turned out to be a boring overlong romance.
I could list more, but I'll leave it at that.