in the corner of the Halo 3: Recon announcement yesterday, Microsoft has made sure to clarify that the "Hell Jumpers" campaign will be released as a standalone product next year (no confirmation of a downloadable version just yet). Halo 3: Recon will not require the Halo 3 game disc and, in fact, seems to include all of the multiplayer components of the original Halo 3, in addition to new maps and Forge options. Recon will also support Saved Films, screenshots, Campaign Scoring, and 4-player co-op. The game is scheduled for release in fall 2009.
Update: Bungie's Luke Smith clarifies that Recon is a "Bungie-made Halo game." In other words, no, it will not be third-person or feature gameplay uncharacteristic of past entries in the series.