Grant Morrison's All-Star Superman is one of the few Superman comics I've really enjoyed. I think he gets right what most writers get wrong concerning Superman. Most of the time, in order to make a threat credible, due to Superman's great power, writers make Superman so dumb he can't see the obvious threat in front of him to allow it to almost overtake it him, only to get out of it in a rather unconvincing manner at the end by beating the crap out of it.
Morrison avoids that mistake. Rather than making Superman square, corny and ineffective, as he often is, Morrison gets to the core of Superman's greatness, which is that he's ultimately an optimistic character who leads by example, and has more faith in humanity that it has in itself (which I think is actually mentioned in the intro). Superman does get tricked by Lex Luthor in the opening, which has very specific and tragic consequences for the Man of Steel, forcing Superman to reevaluate his life and and take care of unfinished business. And while the outcome is inevitable, Superman manages to defeat the opposition over and over again, through his ingenuity and cleverness, rather than with his brawn, much in the same way he does in, say, Superman II and some of the better Superman stories.
Setting it outside of mainstream continuity helps makes it more readable for comics readers. Morrison and the artist give some of the cornier elements of Superman's Silver Age mythology a nice majestic quality that allows All-Star Superman to almost, but not quite, transcend the genre. I like his take on most of the supporting characters, especially Lex Luthor, who is written as a narcissistic psychopath, with a pathological obsession with Superman to the point where he blames Superman for his lack of accomplishment but uses all of his resources in an effort to defeat him. The only character I didn't like is Jimmy Olsen, who just comes across as a third-rate reporter of limited talent who does very well following idiotic trends and writing human interest puff pieces.
Still, a good read for comics fans in general, and Superman fans in particular.