Bungie has managed to do something that eluded George Lucas years ago: create a prequel to a beloved sci-fi series that not only simply works, but is at times better than the installments it precedes. After spending ten hours with the campaign, and another eight or so with the multiplayer, it's already clear that for their exit from the Halo franchise, the developers at Bungie have crafted a fine sendoff in Halo: Reach.
One of Reach's immediate improvements is its storytelling. The Halo trilogy's story has been impeded by both inconsistency (a curious mix of either over-explaining or obfuscating dialogue), and by becoming a fan-only affair overflowing with series technobabble a la Star Trek. Reach rectifies this "inside baseball" feel by telling a broader, more accessible story that doesn't require knowing tons of Halo terminology beforehand.
Don't assume that because you know there exists a Halo novel called The Fall of Reach -- which details Master Chief's origin and his experience during the Covenant glassing of the United Nations Space Command fortress planet Reach -- that you know how Reach the game ends. The campaign focuses on Noble Team -- a UNSC special operations team composed of Spartans (think Delta Force by way of Iron Man) -- and the missions it undertakes. You control the team's newest member, Noble Six (you actually replace the previous Noble Six, whose fate is detailed in the most recent commercial), as Noble Team is tasked with investigating what happened at a downed communication outpost.
Without spoiling anything further, the campaign ultimately unfolds into a grand re-telling of the Battle of Thermopylae, but portrayed from a gritty, ground-level perspective across multiple missions like Band of Brothers, and all done with typical Halo flourish. It's about elite warriors (interestingly, Spartans in both stories) and the sacrifices they make during their last stand against insurmountable odds, and the lasting impact their actions impress upon the rest of the series.