1. The Lord Of The Rings
How could it be anything else? Peter Jackson's vision for JRR Tolkien's sprawling, often impenetrably complex source material was the perfectly executed vision of a committed, passionate fan, with the certain set of skills that could translate that difficult source into a mass-appealing fantasy epic. It really cannot be over-stated how impressive Jackson's adaptation of the source was (along of course with his writing and art teams,) because though Tolkien's power was in his ability to build a complex, and authentic feeling world, with its own mythologies and histories and cultures, those things don't often grip in the source material. Whisper it, but sometimes, Tolkien's writing feels like the insistent, passionate waffle of a history teacher - charming, and interesting yes, but not really appropriate for the big screen. But Jackson and team meticulously pulled out the best parts, casting near perfectly (definitely in terms of the Fellowship) and shooting in an almighty elongated stint that built an obvious and authentic rapport among the cast that shines in the material. The stories and ideological issues are king for Jackson's adaptation, and he never over-stages for dramatic effect, relying on the irresistible pull of emotion to carry through even the most spectacle-laden sequences. That impeccable balance between substance, execution and style is exactly why the Lord of The Rings trilogy outstrips every other and The Dark Knight Trilogy massively in the end.
The Uncharacteristic Low Point? Though they have inspired thousands of words of anger, the extended and over-extended endings of Return Of The King are in no way fatal to the impact of the films, and could have been a lot worse if Peter Jackson had adapted more purely.