The cast has been chosen for the graphic novel that everyone has already told you twice that you should read…
Billy Crudup = Dr. Manhattan
Dr. Manhattan is kind of a big, blue, naked, translucent, pan-dimensional being, so I’m not sure how much it matters who plays him, but I’m still glad Crudup got the part.
Patrick Wilson = Night Owl
To be honest, I don’t remember all that much about Night Owl. He’s practically the main character, but he plays straight man to the menagerie of psychos and damaged goods in this piece, so it’s not the showiest of roles.
Matthew Goode = Ozymandias
Here’s where things get interesting. Yes, everybody thought Jude Law had this one locked and, frankly, he would have been awesome, but I never realized just how good Goode was until I read about this casting and looked back to try to remember who the hell he was.
Here he is in Match Point:

And here he is in The Lookout:

I’ve seen both and I had no idea it was the same guy until I read that it was the same guy. That’s good acting. And that’s why he’s going to make a fantastic Ozymandias.
Jeffrey Dean Morgan = The Comedian

Don’t do Grey’s Anatomy, so I can’t tell you much. Let’s just hope he can play really. fucking. mean.
Jackie Earle Haley = Rorschach

Here’s where Zack Snyder maintains and increases his 300 cred. No one would think of Haley for Rorschach off the top of their heads, but when you hear it, it just clicks somehow. There’s a tortured intensity to Rorschach that Haley can play the shit out of. An unbelievably difficult casting choice, and Snyder nails it.
Malin Akerman = Silk Spectre

From what little I’ve seen of her on Entourage and Harold and Kumar Go to White Castle, I have no idea if she can pull this off (beyond the “are you hot?” qualification). We’ll just have to wait and see.
What I like about these choices overall is that these are not complete unknowns (if you pay any attention to the indie scene – hell, if you’ve seen Little Children you’re already familiar with two of them) and yet none of them are the usual suspects. And, most importantly, they fit. Spielberg excels at this kind of casting, and to look at Snyder’s choices here and in 300, he may, too.

I agree that this is one of the greatest graphic novel stories ever and deserves its reputation. Art was very good, but not great, for example, if it had been done by Arkham Asylum/Black Orchid Dave Mckean. I confess I haven’t been following the movie that closely. Will this be officially sanctioned or unsanctioned by Alan Moore?
From what I’ve heard, Alan Moore NEVER sanctions any of his adaptations. Given the track record (V for Vendetta being the one outlier), I can’t blame him.