Officially, all the Rama sequels were co-authored by Clarke and Gentry Lee. Clarke claimed that Lee did virtually all the writing and he was only a consultant, although AFAICT the only source for this claim was in an interview many years after they were published, presumably after Clarke was aware of their negative reception, so who knows how much of that is true vs. reputation management.

But yeah, they're awful. I read them when I was 12-13 and it was one of my first introductions to the idea that sequels to great books could be so bad (and then for some reason I went on to read the Brian Herbert Dune prequels, which are even worse). Read the first one, and pretend it stopped there.

In my mind, the prose of the sequels were so unlike Clarke when I read them as a teen that it created a long stint of aversion towards spending time on anything with co-authors. I owe Rendezvous a lot though; had I not discovered that book as a kid, there's little chance I'd be reading recreationally today.

The sequel series was one of my favorite sets of books. It’s markedly different from Rendezvous, but I found them an enjoyable read. It was contrived at points, but the series had my favorite ending for a character.

It would seem passing strange that Gentry Lee came up with all the awful bits and the consulting oversight didn't.