I finished reading Alien: Out of the Shadows last night, so here's my thoughts on it.
If I'm honest, I was pretty disappointed. It was certainly written well enough, yet the story didn't really do anything for me. It seemed to want to copy the mystery of Alien by having this huge underground extraterrestrial spacecraft loaded with Eggs, but it just came off as a cheap copy of what we get in the first film. The new characters Lebbon introduced were also pretty bland. Hoop was the only one who was developed even slightly, the rest just faded into obscurity and as a result I found it difficult to care when they died.
But by far the biggest problem I had was with the stupid inclusion of Ripley. Why was she in the book at all? Her presence added nothing to the story, and including her undermined the rest of the plot by introducing needless contradictions and numerous "Oh, come on!" moments of incredulity that were only there so they could shoehorn her in between the films. The part at the end where she begs to have her mind wiped was particularly ridiculous, all I could think was "This is a completely stupid moment that didn't need to happen". Not to mention in the films Ripley is shown to be a far stronger person than that, weeping and pleading to have the bad dreams taken away didn't fit with her character at all.
That all kinda makes it sound like I hated the book, but I didn't. It was entertaining enough while it lasted. It even had some fairly tense moments (mostly in the first half or so). Overall though it just seemed to cause more problems than it fixed. It's certainly not the greatest novel I've ever read, and I doubt I'll ever read through it again, but it was alright.
Also, it didn't explain who wedged the harpoon gun back under the Narcissus door, because it's there at the start of Aliens :P