Halo 3 ODST is an amazing game, with plenty of new, fun, and addicting parts, only check the price tag.
The Good:
A fun campaign with the new ODST's rather then master chief makes strategy and essential for many parts of the game rather than run in guns ablazing, while the new firefight mode is very addicting with lots of fun parts
The Bad:
The price, although the game grows on you until the point where it is worth it the full retail 60 bucks is a bit much, although no regrets from me. Also the campaign is a little short compared to other halo games. Lack of a matchmaking is also a bit of a dissapointment, although you can still play with up to 4 people online in both campaign and firefight
Map packs:
Very fun new maps with lots of good forge details, especially good if you have live, and havnt gotten the other map packs already
In the end, Halo 3 ODST is an amazing fun and addicting game with plenty of new and enjoyment, despite a few flaws that are simply expected from previous games