What is Halo 3: ODST?

[Adam S]

is ODST an expansion to Halo 3?
or is it an entire new game?
does the CD have everything from the original Halo 3?
can i technically trade in my Halo 3 for ODST?
or should i keep both copies?
will there be any new DLC? (since i have all that is available right now)

please and thank you to whoever gives the best answer.

 

[aauron34]

Halo 3:ODST was originally planned to be a campaign expansion to Halo 3 but they decided to make it into a full fledged game. The normal ODST disc with the new campaign and firefight mode while there will be a second disk with EVERY Halo 3 map ever made including 3 new ones. You should only keep the normal Halo 3 if you want to play the Halo 3 campaign because I believe the second disk will not have the campaign on it. I hope this answers your question.