I'm normally one of the first to decry a Disney adaptation of something. Pocohontas still makes me shudder, and that second one that was supposed to be an answer to the critics of the first was twice as bad. However, I have to admit that their version of Tarzan is one of the more satisfying incarnations of the character. That is, aside from the Saturday morning cartoon that was on in the early 80's. I remember little about it other than it was "must see" tv for me and that there were robots. Cheesy floating robots, which I have no idea whether they're in Burroughs' original or not. This is the guy that gave us all those Mars stories after all. So it is quite possible as adaptations go that one wasn't very good, but I have this lingering impression that it was. (The Wiki gods back me up on this, after a cursory look-up.)
Anyway, while the first half of the Disney version is a ways off from the source (though certain elements, such as Tarzan smearing himself with mud to hide his skin, are in the original if memory serves), and while there are notable omissions such as who really kills Tarzan's parents, in spirit I have to think the movie is one of the better adaptations of the myth. Thanks in large part to the ability of animation, it's one of the few where Tarzan moves the way you expect him to having read the books. This is not to say it's perfect, just that as an adaptation it's far more satisfying than some of the others the House of Mouse has put out.
Another adaptation I watched earlier was much more faithful to the spirit and the content of the original. Of course, that was an adaptation of a graphic novel that was, to begin with, somewhat sparse. 30 Days of Night was originally intended as a screenplay anyway, so the transition from comic media to film was perhaps not a difficult one, especially when you factor in the visual nature of both medias. However, plenty of other comic/graphic novel adaptations have not done well, and the record with non-superhero (or even less well-known, or rather less well-marketed superhero) tales is hit or miss. This was one that satisfied in much the same way the original source had. It wasn't particularly visionary, or innovative, but it was fun.
Which, I suppose, is what I look for in an adaptation. (The Bourne series doesn't count, cause aside from the title and initial premise it's essentially a different character and storyline.) All I ask is that it hits the same notes the original did, and if it can do that, even if it isn't 100% faithful, I can live with that.