by Ian M. Banks
The first book in The Culture series and a really solid SF read. 9/10 would read again.
One common SF trope is that all the aliens encountered are human-ish perhaps just with green skin, an extra arm, or some weird rituals. While this books follows this trope for the most part, there are a few species introduced that are are so different we can't even understand their motivations. And this plays some role in the story which is interesting.
The main story is about a war between The Culture and another species it encounters. Even though the next book in the series isn't a sequel to this one (they just exist in the same universe at different times), I would recommend reading them in the correct order (not what I did) since the main character in this book is fighting against The Culture. This will give the reader an interesting perspective on The Culture when you read the second book.