Babel-17

This isn't hard scifi, and for that matter it isn't hard linguistics either. That said, it is a wonderfully different take on a standard space trope, alien invasion.

This short tale manages to throw strange concepts (discorporeal crewmembers, enemy detection through the senses, and many others) into a world with alien invaders and pirates. The idea of linguistic mind control preceded Gibson by more than 30 years. See previous comment about hard linguistics, and the characters are a little flat, but overall a great story.

According to the back, "this novel established his reputation", and it won the Nebula and was nominated for a Hugo. This tale also holds sway on many top science fiction lists. All well deserved. I selected Delany in general and this book in particular to satisfy two reading challenges this year, one for unread Grandmasters (short stories not with standing) and one for the Masterworks of Science Fiction and Fantasy.