I would easily have given the book 5 stars, but a few things had bugged me while I was reading, and I think I'm just gonna list them here before talking about the great ones.

Spoiler

First, the John/Teyla relationship. This is quite a personal issue, actually, depending on whether or not you like the ship in the show. As far as I'm concerned, I don't, not really; I prefer the John/Elizabeth ship, but this is the fangirl talking. Still, for me John and Teyla are just friends, so you could guess that I wasn't very pleased about the turn of events.
Secondly, I had found the way the Wraith culture and customs are handled in the book very... disturbing. I mean, calling a Wraith "Snowflake", or "Dust"? I remain very skeptical about this, let me tell you. We weren't given much hindsight about the Wraith in the show, their way of living and such, and I guess the authors just invented that part. Their names just don't reflect their characters, or the way they behave (eating humans and all), it just don't fit. I've tried to guess why they gave such names to beings known to be monsters, but to no avail...
Some characters were also weirdly portrayed, in my opinion anyway. I liked the character of Jennifer Keller in the show, while in the book I disliked her. I disliked her argument between her and Ronon in the cave, it felt kind of wrong, and Ronon was clearly not happy being with Jennifer, which I found a bit weird, too.

But on the whole, it was a very good book. The general plot is near excellent, and I found myself engulfed in the book without being able to put it down until I read it from cover to cover. I found the story with Dr Robinson quite refreshing, it added a fresh point of view to the events, from someone new to the city, and I liked it.

Long story short, the book is really worth reading, if you're not that bothered by little details that may seem strange.