From the PlanetXbox360.com feature review:
"The Halo franchise is something of a gaming phenomenon, selling more than 27 million video games over the course of its fairly short lifetime. It has become the flagship series for Microsoft's consoles and helped move developer Bungie into a top-tier level of creative power. A couple years ago the release of Halo 3 broke more entertainment sales records than any video game before it, making sure the general public knew the power of interactive media. Adding the word "Halo" to any product will make it a commercial success, some more than others, but still topping charts everywhere. Books, video games, toys, animated movies (coming next year) are only a few examples of the types of products that the Halo franchise can produce. One of this year's biggest releases on the Xbox 360 platform is the supposed last entry in the franchise from developer Bungie and first-party publisher Microsoft Games, a prequel going by the name Halo 3: ODST.
It may not be something entirely revolutionary when it comes to gaming entertainment but for us Halo 3: ODST is the best game (and most complete) in the long-lived series, hands-down."