That's because the movie was also so ****ing well edited, and the actor was truly frightening and crazy! Heath completely disappeared in the role. I couldn't find him anywhere. I only saw the Joker. Heaths delivery of lines was unbelievable & shocking in every single one he spoke. His acting was frightening in every way possible (the oscar was fully deserved). And about that editing. Something that made a scene like the one described above work so brilliantly (like the rest of the movie), had a hell of a lot to do with editing as well. Right after he spoke those "LOOK_AT_ME!" words and turned the camera around to continue with his "See! - This is how craaazy batman has made Gotham..." etc. It truly send C-H-I-L-L-S and utter fear down ones spine, when letting it sink in. And as we all know, the Joker then proceeded to kill this poor victim, whom most intentionally (demanded/directed by Nolan) played out his part as a sort of little naive child with only the best intentions (brilliant way to go by the way, when digging for sympathy). We hear this poor bastard scream in helplessness fear, as the camera flickers uncontrollably around. The audience are left thinking - what in the HELL is the Joker doing to him just there!? Your mind starts imagining unpleasant things (things not appropriate for a PG-13 rating!). All while the scene abruptly cuts to a completely silent panning over-the-city view. PURE_genius editing right there! The thing is that you kinda, sorta want to laugh in that sequence, when the Joker is toying with this victim, at the beginning. A few chuckles was heard in the theater when Joker pulls off the victims mask holding it up in front of the camera, going "Wuhuhuhuhuuu!". You sorta chuckle, up until the "LOOK_AT_ME!" part. From there on no one dared to laugh. It just felt wrong. It was suddenly too frightening and too unsettling. I personally never heard one_single audience member chewing pop-corn from there on during that sequence (and I saw it 5 times). Every one, in every theater (going out on the limb here, I guess) was silent. No laughter. No talk. No nothing. Just complete and utter silents. And it was all due to respect for brilliant filmmaking and editing, at its absolute best.
I get chills every time I think of TDK and about Heaths performance. Now, when talking about Spideys next big-screen adventure, I'll say this. I believe that Fox's Electro will be great, I really do! But I don't think he'll hold a candle to Heaths Joker. These things just don't come along that often. Nor do I believe that Amazing-2 will be better than TDK, and that's for several reasons. But I am definitely hoping for the absolute best spiderman film ever though!