For the record I've only read about 3 real sci-fi books in my entire life. The other two won a lot of medals, were extremely popular, and were very good, but nowhere near as good as Nighteyes. It's a wonder this book is so little-known. Ah, the injustice of the world.
It's actually kind of like two books. The first half is very effective horror (very much like the movie Fourth Kind) that will scare you unless you are one of those silly people who don't get scared by paranormal things. The second half is completely different but equally enjoyable.
In fact I think the Fourth Kind copied a lot of this book, but maybe that's just me.