Just a quick note here to let you know that Halo 3: ODST will be released on PC through the Master Chief Collection on September 22. This marks the fifth installment of Halo: The Master Chief Collection that will be released on PC. It follows Reach, and Halos 1 through 3.
Included in the release is a fully remastered campaign. There is also the wave based ODST Firefight mode that a lot of players loved.