So I'm rereading All My Sins Remembered by Joe Haldeman. It's very nuanced. A very well put together little bit of science fiction. The universe that it paints is subtle and complex, but Haldeman doesn't fall into the trap of putting in too much exposition.

Basically, the main character, Otto McGavin, is a Anglo-Buddhist who has been trained as an assassin for an interstellar government called the Confederacion. He doesn't really like what he does, but he's too good at it for them to let him stop.

You should read it. Find a copy. It was written back when people still knew how to write science fiction (David Weber my ass...).