I can see why this caused quite a stir when it was published. The still-controversial views of sexuality and freedom are shocking to read, and some of the statements made by the characters are downright appalling (I'm looking at you, Jill.)
The thing is, I can understand when a character is making a statement rather than the author him/herself. Still, there were plenty of times when it seemed Heinlein was talking through his characters. If author-insertion wasn't his intention, it certainly seemed that way.
Since I am a fan of science fiction and oddity in fiction, I enjoyed most of the story's aspects, especially the beginning. Two beings on the run, an alien and a human who is both frightened of the alien and yet has an instinct to protect it. A government conspiracy. Knowledge seen as a dangerous entity that must be silence. Thrilling stuff.
The best thing about the character of Jubal, who most seem to think is based on Heinlein himself, is that he wouldn't allow anyone to manipulate him or Mike, the seemingly-friendly alien. I enjoyed this, but it only seemed to last for the press conference in which Mike showed himself to a curious world.
Most of the rest of the book was proselytizing, which I didn't care for. Even if I agree with something, I don't need to be preached at, even if it's done through fictional characters.
Overall, I'd say this is worth a read, if not just for the cultural impact it had and still has.