I didn't read this until last year. I saw the film about six months later. I'm a new convert still radiant with that 'just converted' glow.
Along with the Sandman graphic novels this is my favourite work in the medium (Zenith and Preacher get honourable mentions). Watchmen wins over all of the other candidates in ambition. This is a work of vast ambition. It doesn't deliver on every level, it isn't perfect, but it contains so much that succeeds, and comes so close to fulfilling its promises that it would be churlish to mention any failings.
Alan Moore is a great writer. He's not a great writer for comics, he's a great writer period, who happens to have made the graphic novel his medium. Watchmen is at times literary, funny, erudite, tragic, exciting, intriguing... it's written for intelligent grown-up readers.
The plot sprawls, it's convoluted, it spans generations and a large cast. What keeps it together are the deeply personal stories on various scales. Its scope was what kept it from the big screen for so long, and in truth the movie (whilst good fun and well done, I thought) is just a 2D projection of this complex multi-dimensional work. That same complexity is stopping me from doing it justice in this short review. Rather than try I'm just going to back off the grandiose praise and return to the punchline:
This is a fun read. It's exciting. The artwork ROCKS. It's as deep as that hole Alice fell down, but you never notice you're falling. Pick it up. Read it with pride. If someone sneers at you for reading a comic-book... hit them with it. It's nice and fat!
You can go and 'like' my review on goodreads, if you like.