Of the first three Torchwood spin-off books ("Border Princes", "Another Life", "Slow Decay"), I think this is the strongest one. In it the Torchwood crew have to face several problems at the same time, unlike the TV series where problems conveniently appear at a rate of one a week, and the book studies the characters under stress.
The book also does a good job of fitting itself *into* the TV series without having to follow fixed rules for which characters will survive and which won't (in particular James, as other reviewers have mentioned), and yet it does NOT use a 'magic reset button' or 'it was all a dream' device, for which it should be praised.
Clicking the 'Dan Abnett' link on Amazon suggests that he's a seasoned writer for other tie-in books like Warhammer 40,000, and the battle scenes in this book are well-written. It's quite a masculine book, the up-side of which is that the book doesn't spend too long on the Gwen-and-Rhys-problem that "Another Life" got itself wrapped up in. Personally I found the Gwen-and-Rhys-relationship-breakdown the weakest written and least engaging part of both the TV series and the other books, so I'm grateful that this book doesn't dwell on it.
<geek mode> There is a bit of a plot contradiction between this book and episode 12 of the TV series, and Toshiko's character is very different to her TV appearances, but those are minor niggles. <end geek>