It should be pointed out that this story is written in the style of most silver age comic stories, but with a much darker tone. Many of the main Superman staple characters die in this story and it can come off as depressing for anyone who loves Superman and all of the mythos attached to the character, but it was very well suited for a "last" style story.
Appearances are made by almost any big name character from the silver age of Superman including Bizzarro, Luthor, Brainiac, The Legion of Superheroes, Lana Lang, Lois, Jimmy, and even Krypto, among others. If you're unfamiliar with Superman comics, some of these characters might appear foreign to you (the Legion was for me as I've never read anything with the Legion in it) as they aren't fleshed out too greatly beyond their stereotypical features.
What I found that I enjoyed most about this story is the strain that is apparent upon Superman as he tries to protect all of his friends and loved ones from the wrath of the combined power of many of his past enemies. You can feel the stress that he's under as well as the care that he exudes for those around him. Moore writes him perfectly as a man under pressure but determined not to fail.
Legendary artist Curt Swan contributes the art for this story and he captures the mood of Moore's story perfectly while still maintaining a silver age feel. Personally, I have never been too big of a fan of the silver age style of art, but in this case I found that I really appreciated it simply because it made me remember that Superman has a much longer history that I usually remember.
For anyone that is a Superman fan in the least, this story should be required reading. Moore demonstrates perfectly how to write a character that is often very hard to tell a story about because of his immense history and very narrowly defined characteristics.