I really liked these novellas:

3 stars
The Scapegoat, by C.J.Cherryh
The humans were at war with the elves. The elves had started it by accidentally blowing up a human ship. So then the humans retaliated, blowing up an elves' ship. then there was no stopping the war, each side killing more and more of the other side. Until finally one day, the elves came up with a way to stop the war.

5 stars
Seasons, by Joe Haldeman
An expedition had already gone to the planet and had spent a year there. The native inhabitants were Stone age type beings, laid-back creatures who were welcoming to the members of the expedition. The members of the expedition had got there in late summer, and had left after a year. The thing was, the planet's year was more than three of our years long. The last expedition was 10 years ago; the new expedition were to stay for the whole planets' year, and continue to study, and live with the natives, equipped with only the same tools the natives had: a stone axe, and a spear. But something happened that the first expedition could never have had time to observe: They found out the natives changed behavior as the seasons changed. Not for the better. I love Joe Haldeman's work.

4 stars
Cordón Sanitaire, by Timothy Zahn
The planet Pallas had been settled before, as proven by the ruins, but why and where had the settlers gone? The native tarsapiens, something similar to our chimpanzees were herbivores docile enough to trap and study, until...one day they attacked the scientific team. ( )

All the novellas are characteristic of the author's works, and present interesting worlds and moral dilemmas.
Haldeman's had more graphic sex and violence than suitable for young readers IMO.
Zahn, as usual had a sneaky twist, and Cherryh had a philosophical one. ( )