The first one has a few nice bits (but so, so few), but they're so bad, and so badly written, and so undermine the magic and majesty of the first book, and the final revelation when we discover who actually built the Rama spacecraft is so hackneyed and underwhelming[1], that they're some of the only books I have genuinely regretted reading.
And I've read some Piers Anthony and late era L. Ron Hubbard!
I really have no idea what Clarke was thinking.
[1] Spoiler rot13'd: Vg gheaf bhg gurl jrer ohvyg ol Tbq.
The "sequels" are something else entirely - boring and a waste of time.
It just occurred to me, though, that 2061 (and its villains) do not have a coauthor, although I don't know why that's important to you. Sorry, but your claim that he didn't write villains is just a little silly, and his view of humanity was a little more complicated than "positive."
We haven't even got to the short stories. If you've got a few minutes, read Hate and reconsider your thesis: https://books.google.com/books?id=hbAqAAAAQBAJ&lpg=PT13&dq=h...