If The Bucket List were remade and starred Superman this is kind of what you'd end up with. Its a great story and despite the overwhelming lack of action, the substance makes up for it. And despite my familiarity with the comic off of which All-Star Superman was based, I still cried at the end. A great story, great voice casting and great animation. What Superman Returns should've been.
2-3. You can sort of tell it's an adaptation of a series of comics. It doesn't extrapolate the full substance of each individual story, but the sort of abstract root sum of each story, combined together, makes for a movie that has enough impact per vignette to make for an above average Superman story. It's a series of Superman thought experiments sort of loosely tied together by the main story thread, if you will.
Adapts the greatest Superman story I've ever read (Grant Morrison and Frank Quitely's series of the same name) into an animated feature without losing much of the quirky unusual Morrison elements you'd expect. It's a thought-provoking story that proved to someone like me, who's always found Superman too overpowered to be interesting, that it can be that exact trait that makes him a compelling character.