Not quite what we all expected, but still a great game. Don't listen to the negativity for this game.

User Rating: 8.5 | Halo 3: ODST X360
You've probably heard a lot of negative hype for ODST....
Well, it's in good reasoning. This is a great game, but the people who bash this game have a good reason to do so. But others find it good like I did. Hardley anyone finds it amazingly awesome, but it's still worth a try.
The main Campaign takes place between Halo 2 and Halo 3's storylines, where you play as an Orbital Drop Shock Trooper (ODST) who is trapped behind enemy lines in New Mombasa, looking to see what happened to his squad.
You've probably heard people saying this game is trying to imitate Gears of War, with the Horde-Like-Firefight mode. Well people who say that aren't even thinking too much...
Left4Dead had survival, which is essentially Horde mode and no one cared.
Castle Crashers had Arena, which is essentially Horde mode and no one cared.
But when the new Halo game has a Horde-mimic, everyone has a huge uproar since Halo and GoW are at war for the top seller.
One more similarity, which did slightly anger me (since they kinda did copy here) is where there's an Achievement to do something so many times and when you do it once, a little square shows up at the side saying how many times out of how many times you've done it.
Firefight mode IS AWESOME. It isn't Horde. It has more aspects of a survival game then Horde. In Horde it's just endless Locusts and every once in a while they get stronger. In Firefight, skulls get activated, Reinforcements come, Ammo is dropped, you have lives for the team to share, and many other team aspects.
The Campaign is slightly short, which is the main reason people bash this game the way they do. It's about 4 hours, mission wise if you actually try to kill enemies. If you just run past as much as possible, it'll be more like 3 hours. But the open-world aspect of New Mombasa makes it in the end about 7-9 hours. Luckily, the story is interesting enough to keep it strong.
You're going to have to remember this to keep you from not destroying your ODST disc: YOU ARE NOT MASTER CHIEF!!! YOU'RE NOT A SUPERSOLDIER!!!!!
The reason I say this is because you're a lot weaker in this game. You're shorter, slower, can't jump as high, and can't take as much damage.
You don't have the exact same "Shield" aspect as you did in previous Halo games, but it is very similar. They call it "Stamina" mainly because they can't say shields since you're not the Chief. It works practically the same way, though. And once your shields are gone, you take damage from your health, which will eventually need to be replenished at a Health Kiosk.
I never thought this could be possible, but ally AI is even worse than in Halo 3. Especially in the driver (of a Warthog, for example). I hopped in the turret, so I could get the enemies. A Marine hops in the drivers seat and goes. I thought my disc was broken because of how dumb it was. It would go, stop, run around in circles for a bit, go backwards where you already were, run into the middle of a heated battle and just sit there, and much more badness. Luckily, turret Marines are slightly better, but not near as good to make up for the very very lousy drivers.
Campaign and Firefight are four-player online co-op, two-player splitscreen.
ODST does not have its own seperate multiplayer. Remember, this is an add-on to Halo 3 to tide us over for Reach. That's where the second disc comes in. It features all of the multiplayer goodness of Halo 3, including three new maps along with any or all maps you didn't buy, even if you don't have Xbox LIVE.
The second disc essentially is Halo 3, just without the Campaign. That's it. And we won't miss that too much. So if you want to, you can sell your Halo 3 disc now.
There's not really separate armor permutations like in Halo 3, either. You unlock characters by doing certain things and can play as them in Firefight, for instance with the Srgt. Johnson character for pre-ordering customers.
The Vidmaster Achievements are a load of fun, and I'll be honest, is one of the biggest reasons I haven't put this game back on my shelf yet.
They're at the perfect level of difficulty: Hard enough to where only truly skilled players can get them, and easy enough to where you're not very frustrated.
One is to beat any mission on Legendary difficulty solo while connected to Xbox LIVE without firing a single bullet or throwing a single grenade. Melee and splatters only.
Another is getting to the fourth set on Firefight on Heroic four-player LIVE co-op, which is loads of fun.
Lastly, is to beat the last mission of the Campaign on four-player live co-op with the Iron skull activated and without driving the Warthog or Scorpion (this Achievement is in reference to Halo 3's Vidmaster: Annual Achievment).
Once you get all the Vidmaster Achievements in Halo 3 and ODST, you can sport some of the coveted Recon armor everyone's talking about.
This game's lag is like the Marines in this game: I didn't think it could get much worse than it was in Halo 3. The lag is pretty bad, especially in Firefight with a lot going on. I was just about to get the Vidmaster Achievement in Firefight and got disconnected. Total bummer.

Overall, I'd say that unless you're a true Halo fan, this is a rent at least. If you rent it, then you'll probably want to buy it, and if not, everyone has an opinion.
This has been my opinion.
Thanks for reading.