From the FAQ:
Will the Recon campaign content or the other multiplayer maps be available through Xbox LIVE Marketplace?
Beyond the Mythic Map Pack early next year, there are no plans to release other portions of the Recon package outside of the retail box.
So the “surprise” that Halo owners will receive certainly isn’t downloadable content from the sound of it.
For everything Halo 3 Recon related, click here.
By Mike Bowden