Campaign is mostly entertaining and Firefight is nice.
THE GOOD:
+The graphics are very good. In the second disc, original Halo 3 multiplayer, the graphics may look a bit dated though.
+ONI Alpha site mission. This campaign mission is absolutely awesome.
+Data hive mission. This campaign mission is absolutely awesome, just like the Alpha site. It's a very linear tunnel level, you always know where to go and there are lots of health packs.
+Firefight mode. The concept of Firefight is fairly simple. You encounter wave after another of tough enemies, and offcourse, as you progress, they just get bigger and badder. The melee enemies with the gravity hammers (i don't know their name!) are absolute nightmares, but otherwise it's very entertaining.
+Multiplayer disc. Even if you're not the biggest fan of Halo 3 multiplayer or you already have it, this bonus disc is pretty nice since it includes all the map packs for it. Certainly not the best online shooter on consoles, but you be the judge on that...
THE BAD:
-No matchmaking in Firefight. In my opinion, this was a BIG mistake by Bungie. If you really wanna play Firefight, you need to invite someone to your party or be invited. Sorry Bungie, but none of my friends own this game, and i'm not gonna send game/friend requests to random people, cause i'm not stupid. Failure!
Just cause this is an Xbox360 exclusive, doesn't mean it's a horrible game, PS3 fanboys! If you want to talk trash about a game, you actually have to play it first!!!
So overall, ODST is a solid and fun package, with an entertaining campaign and a fun new game mode.