In a way, this book is like a reflection of the second Alien movie - it meshes nicely with the universe it intends to represent, yet can stand alone as a fully developed and fully functional product.
The Aliens Colonial Marines Technical Manual attempts to flesh out the purpose, function, activities, and equipment of the Colonial Marines, the main military force of the human side of the Aliens universe. It does this admirably, giving depth to not only quite a few things within the movie (such as why the Lieutenant stays in the APC during an op, and how the pulse rifles, dropship, APC, and gyro-mounted rifles function), while giving background on the Colonial Marine military force as an entity, giving additional depth to an already well-defined universe.
I especially enjoyed the parts of the book that weren't even hinted at in the movie, but managed to link up quite seamlessly with the universe that the film is set in. And while I'm no biochemist, I thought the sections written about the scientists theorizing on the existence of the Alien itself were quite interesting, and could almost imagine them taking place in a contemporary laboratory or think-tank if we were suddenly confronted with the serrated, black, acid-spewing horror that is the Alien.
Stylistically, I thought the book was set up admirably, though the extensive use of the Courier New font throughout the book was somewhat trying for me. Of problems, this particular one is of small consequence, and overall, I felt the design and layout of the book was effective and polished, something that is lacking in a few of the newer books of this style that I've seen.
While I originally bought the book because I thought it was an RPG supplement, I have to say that I'm quite pleased with the book itself, and would recommend it to anyone who is a fan of the Alien series of movies.