This is a remake of the Dark Matter book for Alternity, and it is still a fantastic gaming setting. If you like X-files or any sort of conspiracy theory alien invasion book, this is the one for you. This book incorperates magic, psi, high tech, alien species, even extra dimensional creatures all seamlessly.
Reasons to buy this book:
1) Fantastic new rules, feats, classes, etc. This book doesn't dissapoint there.
2) Brilliant art. I know, I know, gaming isn't about the art, but this book has art second only to some high end WOD books.
3) It's very true to the original Dark Matter from Alternity. I played D20 modern for years using the old Dark Matter book and transfering evertying to the D20 system. The original book is more thorough, but this one has every major thing you'll need in it, and you won't need to juggle between gaming systmes to do so.
4) The timeline of the "true history of the earth" is really brilliant. All you need to do is pick a date on there, and you've got yourself an adventure. (A few years ago, we ran what we called Dark Matter 1942 and set the entire campaign in WWII at the birth of the OSS and the downfall of the Nazis who really weren't quite human...)
5) The Hoffman Institute (the group your characters are supposed to work for) is well thought out, and it's founder Dr. Nakami ends up being a very interesting character when you put him in the game. Normally, I hate this type of thing and come up with my own hooks, organizations, and NPCs, but this stuff is so well done, I used it all.
6) This is VERY well researched and thorough. If there is a strange place (there's a whole atlass of strange places and their histories in this book--very cool!), and odd event, or a mythological creature anywhere in the world, this book somehow manages to weave it in to it's all encompasing conspiracy. Vampires? Sure. Big foot? No problem. Gray aliens? It's got you covered. Everything to Tesla and Tanguska to the Masons and a moon base are tied in here!
Weaknesses:
1) The only one I can think of is a lack of enemies in a creature section. Having said that, however, most of the key creatures and aliens you'll encouter are already published in other D20 modern creature suppliments, so they're out there! Go buy the menace manual, and you'll be covered.
2) The original was a real no-holds-barred gaming experience. The PCs were never safe, and even minor creatures could kill the most advanced of characters. This led to some real spooky and intense gaming moments as players were genuinely worried about their characters. The D20 translation isn't quite as nice here. Your 15th level tough character is simply NOT going to be threatened by a gun or even a Weren. Even in a fantastic setting, realism lends a lot. I'd suggest playing it in the D20 Cthulu system for some more brutal rules and less powerful characters.
All in all, this is a book like no other. If you like aliens and modern day conspiracies, this book will change your games forever. I've run two full Dark Matter campaigns now, each lasting a few years, and I'm bearing up to do my third. This is, quite simply, as good as gaming gets!