I've never really liked the portion dealing with the aliens, not because it was published as my own material is not (and since Fox does not acknowledge the alien material in the book as canon I'm not concerned), but more from a writing stand point. It feels like a forced add-on to the book - a book, IMO, that would stand well enough on its own with out the alien material. That said, I have used portions of alien related material as a springboard for my own work. There are a few interesting ideas which lead me down some avenues of thought I may not have otherwise traveled. And in other cases I disagreed with something and it forced me to find something else that worked.
The rest of the book is very solid. There are a few things that don't make tactical sense, but then it's not like there isn't already a precedent for that type of thing in existing military institutions. And I seem to remember the USCM side arm being different in the book than in the film - but I could be wrong (it's been awhile since I opened it). I think the book has a picture of a S&W M-39 (Vasquez's side arm) as opposed to the VP70 (the side arm seen on Gorman, Apone, and others).
The book has also been adopted buy the USCM community at large (of which Harry Harris is a part of) as canon for costumes, props, military history, and military structure. Interestingly enough the alien biology portion of the book is usually ignored here too.
It's an entertaining read on a different end of the ALIENS universe. I recommend it.
