Excellent hard first contact (of a sort) sci-fi, especially because Clarke was savvy enough to realize that sometimes, not every question -- and, perhaps, few questions indeed -- need to be answered to craft a good story.

(2021 re-read): This one still holds up really well. Still fascinating, as much for the many questions left unanswered as for those which aren’t. A great picture of possible first contact.

This is one instance where the movie is definitely better than the book. Not that the book is particularly bad, but it has subplots that haven’t aged at all well, all of which were omitted from the film.