Batman Begins only gets a little worse once the third act gets in. No doubt about it, but it does finish strong with the scene at the leveled Wayne Manor and the final scene. Nolan finishes off Batman's beginnings strong.
But, yeah with the Dark Knight, it still works. It just works extremely well as a film. You sit down just to watch a piece of it and the next thing you know, you've watched the whole damn thing again. The relentlessness of its tone is what always gets me. That sense of the darkness, the dread to come, keeps me glued to the TV.
I think one of the must underrated aspects that doesn't really get that much attention as it should is the score. It's epic, dark, scary, relentless, slightly skewed, and hopeful all at the same time. It's a masterpiece of a score.
And the damn ending. It gets me every time. Every time, I get goosebumps. I've seen this film well over 50 times since the theatre and it's home video release and that ending gets me so jazzed for the third and final film. It hits you so hard emotionally, what Bruce did, that you want to see Batman prevail in the end so that sense of the coming third film after the Dark Knight title card shows up gets you fired up with the possibilities of what Nolan has in store.
I'm of the opinion that Nolan can't surpass the Dark Knight but it won't be for lack of trying. All I need for the Dark Knight sequel is for it to be better than Batman Begins and thematically finish off this story of Bruce Wayne the right way. That's it. Everything else about the film will be top notch.