Players control The Rookie, a silent character part of a five-man ODST team dropped down to New Mombasa during the events of Halo 2.
The five members are split up throughout New Mombasa, and it's the player's responsibility to hunt down the four others in an open world. Upon reaching one teammate's last known location using new equipment like a PDA, players are presented with a crime scene "such as a sniper rifle hanging from a street light."
From there, a "Lost-style flashback" is triggered and players take control of the missing squadmate for a more traditional, linear Halo level.
Each of those levels is said to last 30 minutes, contributing to Bungie's estimations that the whole game is a "3 to 5-hour expansion."
The ODST troopers are reportedly shorter and slower than Halo mainstay Master Chief, making for a different gameplay experience from Halo 3. The weapons they carry may have an impact on the combat experience, as controllable squadmates include stereotypical "big guy" Dutch and sniper Romeo, who's "kind of a dick."
The magazine gave a fight with an enemy Brute as an example of the different style. Whereas Master Chief could jump over the Brute's head or follow it with his Motion Tracker, the ODST will face a Brute that's comparatively bigger and harder to avoid. "You don't feel like a chump. You feel like a very Capable ODST marine, but it's a different feeling," said Bungie creative director Joseph Staten.
Fans may be pleased to know that actor Nathan Fillion of Firefly and Dr. Horrible's Sing-Along Blog fame will contribute his voice to the expansion. Fillion played a random ODST in Halo 3 and will return to voice one of the four major troopers.