I had a nearly overwhelming urge to laugh at the movie by the end. But then, I wasn't so blown away by poor old Heath Ledger's performance I wasn't painfully aware of how preposterous the Joker's plots were. How sad that an actor who had already done so much will be remembered for this.
Joker as terrorist was pretentious nonsense. As explained very clearly above, Two-Face as a character was nonsense, sold only by Aaron Eckhart's truly amazing performance, a far more impressive (and essential to the movie) achievement than Ledger's. Whole segments of the movie are pointless or bungled.
And the action scenes sucked. They were incomprehensible, except when you realize that many of the cuts were so you wouldn't see
Batman lumbering around in his costume. In retrospect, the movie can only appeal to people who enjoy seeing a Bat vehicle pointlessly but repeatedly slam through walls, without wondering how none of the explosives are detonate or the aiming/firing mechanisms damaged.
I think the particular kind of badness in Dark Knight is shown most clearly in the ferry scene. No one on the ferries has any good reason to believe the Joker is a man of his word. But everyone is written as believing perfect nonsense so the movie can pose a fake dramatic choice, supposedly with existential implications, no less!