Consider Phlebas by Iain M. Banks

 This is the first book in the "Culture" series, which consists of about a dozen novels and a bunch of short stories, which Banks worked on until his death a few years ago.  Banks said that he was tired of dystopian version of the future in sci-fi literature where machines and AI rise against man, so he wanted to create a world where the machines and AI are benevolent, help the humans and protect them.  He built "The Culture" with that basic idea in mind, but also set it in a realistic universe where there are other races, civilizations and alliances which are against the ideas of the Culture and there are brutal, bloody wars. This book in particular is about the Culture-Idirian war, which had close to 900 billion casualties. 

My general idea of the style of Banks' writing is that it is somewhere between Star Wars and Hitch-hikers' guide, the second being foundational British Sci-Fi and Banks is Scottish.  Although technology is emphasized - it is definitely not at the level of Asimov, but more emphasis is placed on adventure, swash-buckling heroes (Horza) who get themselves into difficult situations and the bravely, and by the skin of their teeth, get out of them victorious.  Btw, my personal preference is for short, dynamic, explosive descriptions of fight scenes, but Banks has completely opposite idea, where single fight of 10-14 mins is described over 4-5 pages, with every minute detail described profusely. 

This first book is about a Changer, Horza, who work for the Idirians against The Culture, and Balveda, a Culture Agent from "Special Circumstances" (basically military intelligence).  The Culture has no military and uses no money since it is 'coordinated' rather than 'ruled' by "Minds" which are advanced, sentient AIs which exist in multiple dimensions, think faster than light, and have storage capacity the size of an average planet.  Changers are humanoids which can change their outer appearance (over several days) to ideally represent any other humanoid they've observed.  The lore says they are a remnant of some genetically-modified population from some forgotten war, thousands of years in the past.  They are living weapons, having venomous teeth and nails and can also spit venom. 

Idirians are tri-pedal giants with saddle-like heads and redundant organs for every function, a result of evolving on an extremely inhospitable planet, which gives them biological immortality (i.e. no aging or disease death, but definitely death from being murdered or destroyed in an accident).  They are a theocracy and religion/God is the main pillar around which their society and personal lives are organized.  This makes them natural enemies of The Culture, which is Atheist by nature, and also proselytizing their ideas across the Galaxy. 

There are many adventures throughout the book that Horza gets himself in, like with the Eaters, Game of Damage, Kraiklyn's Free Company, Balveda's infiltration and Horza's escape from Culture's transporter.  Horza is not the typical Star Wars hero, as he is at times selfish and murders to achieve his goals, but we still end up sympathizing with him.  The background onto which he exists is much more murderous and self-aggrandizing, so he comes out as a moderate by comparison.

Horza dies at the end.  His entire species of Changers is completely destroyed by the end of the Culture-Idiran war and does not figure in future books, except as a remembrance.