This was the bookgroup book and the only one of the 13 of us who liked it was our leader/fan/librarian. It seems very cracked, like it fell and was put back together but was missing parts. I figured partway through that maybe Clarke couldn't write and turned it over to Pohl, and Wikipedia told me so. When I finished the book, a postamble told me so, too. Clarke handed some pages and notes over to Pohl and he decided if things were all right. The book had been finally written three days before Clarke died.
This is almost always set in Sri Lanka -- where Clarke lived -- and has really almost two stories that are kind of shoved together. We thought that the Sri Lanka story was primarily Clarke's, while the alien part was primarily Pohl's. There were people introduced who we never saw again, people who just disappeared, and people who appeared at the right moment, as if they'd been there before.
I don't recommend it.