After years of waiting until I was in the right mood and not especially preoccupied with specific other versions of Superman, I finally bought this and read it over the past week. It pretty much lived up to its reputation, and is definitely one of the best Superman stories I've read. I take some issues with how the alternate timeline worked, though. Most of it just has to be explained by Zemeckis-Gale "time works like a river that tries to correct itself if its course is changed" logic - and that's fine - but I would've preferred it if everything had been shown to be a direct result of Superman landing in the USSR, rather than just "this is this story's version of Batman", etc. Why isn't Bruce Wayne Batman? Why would a(decade-or-two younger) random Soviet kid whose parents were murdered by the politburo grow up to be a bat-themed tactical genius? It would be different if mainstream Batman was traditionally inspired by mainstream Superman, but that's never been the case, in fact he often precedes him by a bit. So what happened to Bruce and the Waynes?
Wonder Woman on the other hand worked great in that way. Hal Jordan and his backstory were brilliant, an excellently-realized story highlight. Was it that he was powerful enough to personally create a few dozen other power rings? That could've been clearer, but it's still awesome.
I didn't even notice the change in artist until reading about it in the end notes. I actually like how this caused the art to evolve from a simplified, iconic Golden Age style into something more modern, though.
BizarrUS might be the best version of Bizarro ever, and it took Millar what, like three pages to do it? Some of the other classic villains could've been fleshed out more in terms of how Luthor created them and why they were ineffective, especially Parasite and Doomsday.
I was so glad Supergirl never factored into the equation. I was a bit worried she would at some point. Lex Luthor was of course excellent and satisfying.
The ending though.... I don't exactly get what its significance is other than a huge mindscrew - and it is a huge, incredible, eyes-wide, gripping-the-book-tighter-and-tighter mindscrew - but .... why? And how does it make any sense, given that they established on the same page that the Luthopia colonized the entire Solar System eons earlier, i.e. a bunch of nearby planets and moons with human civilizations on them to send a baby to. I'm not surprised to hear Grant Morrison pitched the ending because it really felt like something out of separate story. What would've felt more appropriate is some future experiment that ends up causing a 12-hour timeshift in the past, landing Kal-El in Kansas creating the DC universe we know(in kind of a tragic way, given how well things had turned out in the Red Son timeline).
Still.... great stuff. The main thing is that even when Superman's become a dictator, it's still unmistakably the same character we all know. The way that Mark Millar somehow still captured and communicated that so well at a point in the story where there're no balloons to save or gee whizes to be said proves how well he really, really gets the person that is Superman, underneath it all, and that's what makes the story a classic.