I think the first thing to say about this one is that it's rife with artistic license. If you can get past that and you love the Eldar, then you'll probably really enjoy it.
As far as readability goes, it's not bad and I didn't ever get bored. There are places I thought the style was clunky and overly introspective, and I personally feel he makes his Space Marines a bit *too* human and not Codex-compliant enough, but then I suppose that's how he's chosen to develop the chapter. As I mentioned, if you're into Eldar then the three books are full of Eldar stuff, very often to the extent that it pushes to one side the Blood Raven plot, not something I think should be the case in a trilogy that's supposed to focus on them.
There's an extra story in this one which he wrote after the trilogy to flesh out one of the main characters, and I think that's definitely worth a look. Certainly, I thought it was one of the better-written parts of the book.
I definitely would not recommend this book to die-hard WH40K canon purists, and there certainly were points where I honestly wondered what on earth the author was thinking with certain somewhat heretical things he has the marines doing (and more importantly getting away with). If you've only played the games and don't really care about that kind of thing though, you'll probably be fine with it.
Overall, I would have given it a 3 star because it's got some fairly decent characters and fun plot in it, however it gets a 2 star because of the poor quality writing, and the fact that it's supposed to be a WH40K book, not an original novel. Why not work within the already rich canon set-up rather than deviating from it?