Hyperion

Brilliant on just about every level, Hyperion IS the quintessential space opera series. Simmons puts everything you'd ever want in a Space Opera (breathtaking action, military engagments in and out of space, faster than light travel, AI, etc), but what sets this series apart from the rest is the deep human themes explored, the cast of emotionally tortured (yet all the while compelling characters), the beautiful prose, and Simmons' ability to seamlessly structure the narrative in homage to Chaucer's Canterbury Tales as a series of interrelated tales told by each character as they march to their doom on a desolate planet to seek answers from a god. If you have not read Hyperion, stop everything and make sure you do. The 'series' is divided into two series -- each having two books. Both are brilliant and both are completely different sorts of stories.