First off, I believe Before Watchmen never should've existed in the first place. Whether or not Alan Moore was screwed over by DC isn't relevant to the fact that Watchmen is a story that should stand on it's own. The subsequent prequels and sequels cheapen the original.
However, while there were some clunkers, most of the Before Watchmen books were better than they had any right to be.
Ranked from best to worst:
Minutemen
--While not as good as it's predecessor, this was the only comic that seemed worthy of Watchmen. Darwyn Cooke gives it his all. It does for superheroes what Boogie Nights did for porn stars and Goodfellas did for mobsters.
Rorschach
-This is a very simple story. Rorschach meets a girl and fights a bad guy who you can tell from a mile away is crazy; But it works. No comic captures the 70s like Lee Bermejo in this book.
Silk Spectre
If this miniseries didn't have the Watchmen name on it, it would've probably been for the better. This isn't Watchmen, this is a John Waters flick meets the Silver Age comics where DC tried to desperately pander to the hippie crowd.
Ozymandias
-Outside of the original Swamp Thing run, I haven't read a lot of Len Wein, but this may be the best I've read by him. However the real star of the show is Jae Lee. The art on Before Watchmen is probably the last great use of concentrated talent by DC in some time. It makes me feel like the artists would be better spent working with Alan Moore on an imprint like ABC rather than regurgitating one of his old properties. A little too biographical for my taste and Ozymandiaz might be a little too cartoonishly egotistical.
Dr. Manhattan
The least offensive of the Strazynski comics. Like Ozymandias, Dr. Manhattan feels less like a story and more of a biography of a fictional character. I liked the very contemplative and scattered nature of this miniseries though. Some of the characters are drawn without faces, which makes you realize why Adam Hughes sticks to drawing covers these days.
Moloch
-I have never seen a comic improve in quality issue by issue so rapidly. Hated the first issue, Moloch was portayed as your cliche sociopath with a tragic past. However the second issue was a very impactful tale about Moloch being duped by Ozymandias.
Comedian
I don't recall much of this comic, except that the narrative was very disjointed. A rare disappointment from Azzarello
Dollar Bill
Any excuse to display Steve Rude's artwork is appreciated, but this is so obviously a cash-grab. In a line of comics that shouldn't exist in the first place, this is the least deserving.
Nite Owl
In the words of Roger Ebert, "I hated it, I hated it, I hated it". Ruins one of the greatest mysteries posed in the original Watchmen of the woman in Nite-Owl's picture and sports what may be one of the worst villains ever to grace the comics page.