HALO 3: ODST wasn't supposed to be this good.

Arriving eight years after Halo justified the existence of Microsoft's original Xbox, ODST was first announced as a mere expansion to 2007's Halo 3—a quick, easy way for Microsoft and Halo developer Bungie to squeeze more money out of their ridiculously popular franchise. But surprisingly, ODST doesn't feel like a cash-in—in fact, it might be the best Halo yet.

Bearing all of the series' trademarks while also nudging its familiar gameplay in a new direction, ODST feels a lot like Halo, a bit like Metroid Prime, and kinda like BioShock. Instead of playing as the series' usual hero, Master Chief, players take on the role of "Rookie," an "orbital drop shock trooper" tasked with searching a war-ruined city for his missing squad mates. Thanks to the Rookie's downgraded skill set (no dual-wielding, less health), humanity's fight against the aliens known as the Covenant now seems significantly more dangerous, and ODST's moody, noir-ish tone creates a richer, darker, and more nuanced experience than any previous Halo. As the Rookie discovers clues from his fellow soldiers, "flashback" levels are triggered—by letting the player take on the roles of those squad mates, ODST provides enough variety to keep things from ever getting boring.

Despite the fact that the Halo series is beloved for its multiplayer mode, ODST is unquestionably a single-player experience—tackling the campaign in co-op mode is possible, but doing so can feel awkward and jarring. That said, ODST does come with all of the existing Halo 3 multiplayer maps (and three new ones), plus a new multiplayer mode, "Firefight," which functions like Gears of War 2's "horde mode": increasingly pissy waves of enemies swarm the players for a more arcade-y experience.

Firefight and the maps are fine, but ODST's sometimes haunting, consistently thrilling campaign is the real draw here, bolstered by solid voice work from Serenity's Nathan Fillion, Adam Baldwin, and Alan Tudyk, and Battlestar Galactica's Tricia Helfer. This is still Halo—Martin O'Donnell's grandly melodramatic score still blares, a lot of things explode, a few thousand aliens erupt in splatters of purple blood—but by trying something a bit new, Bungie's created something that's arguably the quintessential Halo experience.