All-Star Superman is written by Grant Morrison, the author of the previously mentioned Supergods, which I'd completed just a couple of weeks before. The basic premise is that Superman flew too close to the sun and was poisoned by radiation so bad that his cells are dying, and he has a limited time left in which he must complete 12 labours. Each book in the collected omnibus follows him completing one of these tasks.
The book basically reads as every Superman fan's biggest highlights. Dress up Lois in a Superwoman suit and have her fly along with him. Go to the Bizarro world and stop them trying to take over Earth (by, of course, telling them to do exactly that). Save Kandor, that tiny little version of Krypton that he's accidentally trapped in a bottle.
But it also moves on to bigger things: If we really had a Superman who could do anything, what would we want him to do as his final task? Cure cancer. Create life. Make the sun indestructible. And not die.
I thought the book was a lot of fun, and it's easy to follow even if you're not someone who grew up reading the Superman comics. I knew enough of it just from knowing the lore, and I enjoyed it a lot.
Red Son even more. The premise is simple: what if Kal-El had landed in Russia instead of Kansas, and grew up to be a stalwart of Communism rather than a saviour of capitalist US of A? It's a brilliant concept, and one that manages to explore the different Superman who emerges without casting any judgement on either side. It's a brilliant alternative universe story, one where Lex Luthor, a scientific genius in the US, sees the emergence of "the Superman" as the not-so-secret weapon of Russia (in Russia, Kal doesn't have to create the Clark Kent secret identity, and is used instead as a government weapon), and thinks to himself, "Dammit, if only the Superman had landed here instead, I have no doubt we'd have been great friends!" Ha!
Beautifully illustrated (I really liked the artwork in All-Star Superman but loved it in Red Son), this is the one I'd recommend more, although both books were a lot of fun to read.