This book gets a four out of five despite how utterly unlikeable the main character is and a few kind of dated things (the Freudian therapist for instance... though that gets a little subverted by the very end). Mostly because I'm still thinking about the book and having feelings about it 24 hours after reading it. 
 I know there are sequels to this book, but I will not be reading them. Part of what I loved about it is the hopelessly absolute mystery of the alien technology. It adds to the melancholy and terror of the story. I'm pretty sure I'll be rereading this book at some point and I don't need to be thinking about the "real" purpose behind certain gadgets in the space ship and how some random artifact they find is actually THIS REALLY IMPORTANT THING or conversely the alien equivalent of junk food wrappers. I want to keep focusing on the bravery/foolhearty-ness of human beings risking it all for riches and human progress via tools they have absolutely no understanding of. 
 Like The Forever War and Stranger in a Strange Land, it's pretty sexually progressive for its time. There are all kinds of relationships present. Not just straight and not just monogamous. And aside from the aforementioned Freudian junk, it's actually not particularly judgmental or utilized for laughs. Gay characters are just characters that happen to be gay. 
 So yeah, I recommend.