Trang, by Mary Sisson, is a surprisingly clever novel about the world's first space diplomat, dealing with a collection of strange and not always comprehensible alien species on space station. He is assisted, and “assisted”, in this task by a platoon of space marines: extraordinarily tough and rude killing specialists.
The aliens are the stars of the book. Each species is distinctive, and most are unusual. Their motivations range from comprehensible to obscure, which is a good thing for aliens.
Actually, the space marines came a close second. Trang initially thought that they were all cut from the same cloth, but several of them soon revealed distinctive personalities beyond their super-tough violent space-marine veneer.
And it's pretty funny. Not in the intensely silly style of a Hitchhiker's Guide or something, but little things. I was particularly taken with the automatic translator which usually let the characters communicate, but sometimes had to resort to very general terms: "The hull is not made of glass. It is composed of a composition."
Disadvantages: The plot sort of wandered around for most of the book. Trang himself isn't all that interesting.
Four alien species out of five. I'm planning to read the sequel.