If you are looking for sci-fi action from start to finish, then any Warhammer 40k book is probably a good fit. I don't like giant power-armored space marines, however, so the Imperial Guard series is a good place to start. I wasn't sure how this would be, but was pleasantly surprised. Is it high-brow lit? Heck no. But, it is a lot of sci-fi fun and military action with a good story. It was just what I was after.