If you are a Halo fan who somehow never purchased Halo 3, then Halo 3: ODST is a must-have, as it includes all of Halo 3, (minus the campaign) along with the Halo: Reach beta, and the Halo 3: ODST additions and improvements. However, if you don't play much Halo online, or you don't have a lot of friends that do, then you'll probably want to wait for a price drop on Halo 3: ODST, as the campaign is too short to justify a full-priced purchase.
