If you liked any of the Halo games, especially Halo 1, this is a nice throwback for the fans of the series. Stupendous.
Campaign: Holds up to the quality set by other Halo games. Wish it was longer, but that only means it was a great ride. I played it on Legendary the first time through and I plan on playing through it again, solo and co-op.
Firefight: Absolutely fun. I wish you could play it with people in matchmaking, but it's a ton a fun with 3 other friends.
Halo 3 MP disc: A great $ value for those of you who play halo 3 multiplayer. Includes all Halo 3 map packs and original Halo 3 maps.
Halo Reach MP Beta: What's more, if you buy ODST you'll be guaranteed a spot in the Halo Reach MP Beta in 2010. And who doesn't want to see what that game's like?
Conclusion: If you want a new Halo game experience, this one will satisfy your needs. I recommend it!