To given an example, I'll use Zuko. From the perspective of a new viewer who has never seen the cartoon, Zuko's obviously the bad guy who arrests Aang in one early scene. Suddenly a few scenes later he's the Blue Spirit rescuing Aang. I have seen the cartoon so I understand why Zuko is freeing Aang, but what about the new viewer? The movie just did not do a good job of connecting the dots to form a smooth flowing story.
Exactly my point. The desire to do a "faithful" rehash of a 400-minute story in a 100-minute form led to it being so compressed that it was all events, no characterization or meaning. By being faithful to the structure, it lost the substance.
I mean, really, did the movie need the Blue Spirit at all? That episode was basically about Zuko's struggle with Zhao -- he wasn't "freeing" Aang but taking him away from Zhao so that he could claim the glory of the Avatar's capture and win back his father's approval. But Zuko's competition with Zhao is an ongoing thread throughout the story, coming to a head in the Siege of the North, so it wasn't necessary to include that specific vignette in order to convey it in the story. The events could've been streamlined, Zuko's defiance of Zhao coming in the Siege of the North, all part of the same climax.
A truly "faithful" adaptation is faithful to the characters, attitude, tone, and ideas of a tale, even if things like the plot structure or the characters' appearance are altered. I think audiences and studios today are too obsessed with "fidelity" to the superficial forms and thus they miss the point of how adaptations are supposed to work. Adaptation is about change. It's about doing things differently to make them work in a different medium, a different format.