I am not a big sci-fi reader. That said, I've read this 4 times (plan to read it again) and, after finishing book 2, walked through a snowstorm to get book 3.
Note: if you don't want to commit to reading a series, you can quite happily stop at book one. You probably won't want to, though.
Impossible to put down, once first contact is made (you don't have to wait long). *Love* the (very well-developed) characters, interesting world, really keeps you thinking, throws in good suspense and mystery, too. Does not feel like sci-fi at all and is never preachy. Interesting concepts to wrap your mind around, for instance, how do you interact closely with people so different that, though they are a highly social species, have no concept of 'like', 'love' or 'friend'?