I know I'm about five years late to the party, but I just read all of Before Watchmen (for whatever reason) and really wanted to hear what the rest of the comic community thought of it (if anyone read it in the first place). Here's my quick thoughts:
Minutemen- Fantastic, and a worthy spinoff of the original. When I inevitably reread Watchmen, I plan on reading Minutemen first. DC should've started with this one to test the waters. I think people would've been much more open to the idea of Watchmen prequels if this had been the only series to start with.
Silk Spectre- A fun read, with glorious artwork and panel layout, but can't see myself caring enough to read it again.
Ozymandias- Another fun read, that I kind of enjoyed while reading it, but then came to realize that it's literally just full of really lame/lazy explanations for plot points in Watchmen. Ie: Comedian just happened upon Adrian's plan; Adrian decided to be a superhero because he had a junkie girlfriend for few pages that died.
Nite Owl/Dr. Manhattan- These were solid stories, but extremely forgettable imo.
The Comedian- Boring. Dull. Everything wrong with Before Watchmen.
Rorschach- Pure garbage. Almost everything about it sucks.
Crimson Corsair- Started off interesting enough, but became really tiresome. The "twist" at the end was about as bad as "who was phone."
Moloch/Dollar Bill- Pointless.