I've just finished and I'm really not sure what to make of it. Some of the bits regarding experimentation and how it linked in with the lore were interesting, and so were some of the sub-plots, but there was a lot that didn't work.
It seemed like a lot of the action took place 'off-screen', so to speak, and it felt like plot threads and characters which could have been developed instead got wrapped up way too easily, or just abandoned.
I kinda felt like I was reading the novelisation of a TV series, but it was only the middle of the season, and the beginning and end are in other books. I know it's supposed to be a prequel to Fireteam, but it doesn't actually feel like it's setting anything up. If there's more information pertinent to the book in the game itself, that's fine, I guess, but you shouldn't have to buy the game in order to flesh out the novel.