Yesterday I finished John Scalzi's trilogy of interstellar trouble, which started with Old Man's War, continued with The Ghost Brigades, and wrapped up nicely with The Last Colony. As one reviewer mentioned, the books are fairly short, so reading the whole trilogy is a lot like reading one volume of many other trilogies.
It's "hard s.f." with a military edge, somewhat reminiscent of Heinlein at times. The author has a lot of big, interesting ideas. His characters are sharply, but not deeply drawn. The twists and turns keep coming throughout the series, so I'm just going to tell you the opening premise:
People on earth, when they're old enough, if they wish, are allowed to leave the planet forever, in order to be rejuvenated and join the Colonial Defense Force to fight in wars against aliens.
If you happen to like this genre, I recommend the series.
You grow old, and then turn young
In order to be slung
To deadly far-flung wars
Among the stars.