Bungie's latest release in the Halo franchise was first announced as an "expansion" or a "mini-game", one that wouldn't be a full-priced release. As a consequence, many reviews and comments have judged the release of Halo 3: ODST based on its value as a $60 game. It's probably a fair enough judgment for any game, but ODST probably wouldn't see its value picked apart in just about every review and forum if they hadn't announced that it wouldn't cost $60.
They also billed this game as an "expansion", which seems a little unfair to the game itself (and doesn't help the judgment of its price point as a stand-alone game). The inclusion of the multiplayer component of Halo 3 in the box (with three new maps, not yet released on the Xbox Marketplace), plus the fact that it is called Halo 3: ODST and not just Halo ODST, just seem to add to ODST's identity crisis. Is it a game of its own, or just an extension of Halo 3?
The game takes place in the city of New Mombasa, Africa, which is under attack by Covenant forces, the attack that kicked off Halo 2. (The time frame overlaps probably as much as Halo 2 as it does Halo 3 — making me wonder even more about the "3" in this game's title.) You start out as the rookie of a squad of Orbital Drop Shock Troopers — on the butt-kicking scale, they rank way above a normal Army or Navy soldier, but below a Spartan. The squad is preparing to drop into a lone Covenant ship hovering over the city, when an ONI agent joins the team and changes their orders to drop into the city itself on an unrevealed mission.
This game is quite different than the Master Chief story that comprises Halo 1, 2, and 3. Master Chief is all about eliminating the enemy, plowing through Covenant invaders like a combine through wheat. However, Master Chief has the benefit of being a genetically-enhanced soldier with a metric tonne of powered armor.
An ODST, by contrast, is neither biologically modified nor encased in armor. He is much more — for lack of a better word — "human". Granted, he's no slouch. He's the best of the best, as far as human marines go, at the peak of physical conditioning and trained in a wide variety of human and alien weaponry and technology. He can even run at a normal speed while carrying a machine gun turret. However, without the protective armor, an ODST is much more vulnerable to damage. He doesn't have regenerative health, or a motion tracker, or shields, or the ability to dual-wield. In many ways, it's a lot like Halo 1.
There is a simulated sort of "shield-and-health" system like Halo 1. In ODST, the "shield" is "stamina", and it's not measured with an electronic bar but by a reddening of your vision. When your stamina is depleted, damage is taken to your health (which does have a measurable bar). Staying out of the line of fire will recharge your stamina (and clear your eyesight). It's much less resilient than an actual "shield", but it serves the same basic purpose.
Back to the story. As your squad drops into New Mombasa, the Covenant ship jumps into slipspace. (This is the point, in Halo 2, where Master Chief, Miranda Keyes, and Sergeant Johnson follow in the In Amber Clad and wind up on Delta Halo.) The resulting shockwave from the slipspace jump creates an EMP that knocks out the electrical systems in the ODSTs' drop pods, and they crash in various places around the city. You, playing as the unnamed and unvoiced "Rookie", wake six hours later in nighttime downtown New Mombasa, alone.
The gameplay is split here. The nighttime New Mombasa city streets, as the Rookie, have you attempting to find your squadmates. Although the game purports to offer stealth here, even playing on easy, I found that I was unable to avoid encounters with Covenant forces. The battles tend to be much smaller-scale, with patrols of just a few grunts and a brute typical. You're guided to the story elements in turn by a checkpoint system controlled by the city's Superintendent computer (or, presumably, if you wander around on your own, you could discover them in any order). These nighttime interludes can last as little as 10 minutes if you focus on the next checkpoint and go straight there.
Once you find a relic (a damaged helmet, a discarded sniper rifle, an empty can of biofoam), the game shifts into a "flashback" mode, where you switch to the point-of-view of one of the ODSTs that was there, and the events that led up to leaving that item where you found it. These modes are closer to "typical" Halo: more action-oriented, faster-paced, fighting with squads of AI-controlled marines against larger and more diverse squads of Covenant forces. It is through these "flashbacks" that the story comes together.
On the way, you can find audio clips that tell a side-story of a certain girl whose father worked on the Superintendent program, and what happened to her when the Covenant appeared over New Mombasa. It's completely optional (aside from achievements), but it is a good-quality story with about 40 minutes of audio that is highly reminiscent of the "I Love Bees" audio program that preceded Halo 2.
Eventually, the squad is reunited, and, without spoiling the story, the game ends with the squad making a stand against several waves of Covenant forces as they wait for evac. It gives a fitting climax to the battle, while appropriately setting up the Firefight mode.
Firefight is the Halo version of what Gears of War has popularized as "Horde Mode", where you and up to three friends battle cooperatively against wave after wave of incoming enemy forces. Having not played Gears, I can't offer any first-hand comparisons, but I have heard that ODST generally moves a lot faster in that even the early waves give you a significant number of enemies. It increases the challenge by not only adding more and stronger enemies, but by cycling through different combinations of skulls. These are the same skulls that are available in the ODST and Halo 3 campaigns (the ones in Halo 3 had to be found to be "unlocked" for use; in ODST, they're available from the start) that alter gameplay by making the enemies more damage-resistant, making weapons drop with less ammo, and so on.
In some ways, Firefight is a good mode for picking up and playing with friends. It's set up like the campaign, where you pick your squad from your friends (no matchmaking) and you fight against the AI, but it doesn't lock you into a scripted story and make you and your friends choose a subset of an involved story arc to play through.
On the other hand, Firefight's strength is also its weakness in that it reveals just how simple the gameplay is in Halo; and both how much the story is a powerful part of the game, and how shallow the game feels without it. With wave after wave of the same enemies on the same level, a Firefight match can get almost tiring after a typical hour and a half that a good squad can pull off (on the short end), where it's almost a relief when the lives run out and the game ends.
If I had to compare ODST to Halo 3 (which, considering the way it was marketed, I sort of have to), I would have to agree with those that have said that ODST is "less" of a game than Halo 3. The campaign is shorter, and it only has a single, rigid multiplayer mode in Firefight. (ODST does come with Halo 3's multiplayer as a separate disc, but I don't think it's fair to consider that a part of ODST — the Xbox doesn't anyway, as it identifies the game as Halo 3. Besides, if you already own Halo 3, and especially if you've acquired all of the map packs up to this point, the only value added is the remainder of the Mythic map pack that is only available on the disc packed-in with ODST.) However, to judge it on its own, or to even compare it to the multitude of other games that have been released at a $60 price point, I think the game delivers a fair amount of value. The narrative is classic Bungie storytelling, although in a very different format than before. The gameplay feels a lot like Halo 1, which you may love or hate (but you will definitely love the return of the pistol). It's the same, excellent blending of gameplay, story, and music that has made Halo the success that it is. And if the $60 price point still feels too high, about half the retailers out there are already offering the game with deals or discounts out of the gate.