James Blish. A Case of Conscience. Ballantine, 1966, originally published 1958. 188 pages.
The quality of the prose is quite good, but there are some major problems with the story structure. The book has two parts. The first is a lengthy short story, and is excellent. Four scientists, one of whom also happens to be a Jesuit, study an alien planet and the culture of its people, with the goal of deciding whether humans would be harmful to the planet (or vice versa). The second part is an extension of that story, in which the scientists return to earth with a controversial specimen, and it’s kind of a mess. It’s more like a sequel than the continuation you’d expect from the second half of a novel. It abandons the focus of the first part, and on top of that it has very little focus of its own.