In the Black

At the start, this appeared to be a standard space-battles-against-hostile-invading-aliens story, but it turned out to be something very different and much more interesting. The action switches between a couple of engrossing storylines and characters - the captain of a powerful defense force spaceship patrolling the border shared with an alien race, and an arrogant corporate CEO whose multiplanetary company suddenly starts experiencing attacks by an unknown saboteur.

They come together in a satisfying twist at the end. However, the story is very much left on a "what happens next?" cliffhanger, and readers who don't like waiting for next installments may wish to wait until the sequel has been published.