At the time a welcome breath of fresh air from the stuffy, soap-opera-esq Dan Jurgens era of the Superman books (which had more than run its course BEFORE they tried to goose sales with gimmicks like the Electric-Blue Superman), the Jeph Loeb/Joe Kelly era-- here collected up to their big, status-quo revising "Y2K" storyline-- has not aged entirely gracefully.
For one thing, half of the collection's authors are less-than-stellar-- whether its because Jeph Loeb's failings as a writer have become far more obvious over the years ("Big spectacle! Guest stars! Who cares if it makes sense, as long as it's fun?"), or because Mark Schultz was just not a very good writer to begin with. Secondly, there's a lot of dated, "edgy" content here (mostly from former Deadpool scribe Joe Kelly, of course), such as casual sexism, racism, homophobia, ableism... the usual suspects. Third, there's a whole lot of try-hard "coolness" on display as well, in particular with the curt and snarky approach to writing Lex Luthor; characters brag about all the badass stuff they can do to establish how dangerous they are, rather than letting their actions speak for themselves. And finally, the base characterization for most of the supporting cast is inconsistent from issue to issue (and occasionally, they'll have Superman cracking a joke that seems TOTALLY out of character for him).
But for all the things that have aged like warm milk, there are some details that they got right. For one thing, these are the first Superman books that really embraced the new relationship between Lois and Clark: emphasizing their more intimate married behavior, developing their domestic lives together, and exploring their insecurities and fears about married life (the issue exploring Lois's jealous thoughts about Wonder Woman, and the fact that Clark just doesn't see her that way, being the obvious standout here). These books also strongly emphasize Clark Kent's humanity as Superman's defining attribute; we got much more of a sense of Clark as a person, from his farm-boy upbringing to his journalistic leanings and the basic optimism about people that underlies his heroism.
Also, I'm just gonna throw it out there: while it's not my favorite way of depicting the character, the far more stylized art style used for Superman-- culminating in the anime-flavored work of Ed McGuinness, which turned the Man of Steel into a preposterous mountain of rippling muscles-- was a welcome jolt of creativity that shook the character out of a visual rut that he'd been stuck in since John Byrne left the books. The book is full of bright, poppy images that draw the reader right in, even if the scripts they play out are little more than hollow trifles.
This isn't my favorite run on the character, but it was a welcome change of pace at the time it was released, and it made Superman fun again after years of dull stories and creative stagnation. It's the J.J. Abrams Star Trek of Superman comics: a colorful bauble that skirts by on charm and style alone.