One of the best "expansions" I have ever played.
For those of you who don't know, Orbital Drop Shock Troopers (ODSTs) are the best of the best, as far as normal humans go. They're a bit crazy, and likely so, as becoming an ODST is voluntary, and dropping in the HEVs has a chance of death every time, either by impact, or enemy fire.
You play as the Rookie, a new member of an ODST squad. In the squad, you have Mickey, the demolitions expert and funny guy, Dutch, the heavy weapons expert and tough guy, Romeo, the sniper and smart-ass, and your sergeant, Buck. With them is an ONI spook captain named Veronica.
After the orientation, you are dropped right into the city before the slipspace jump. Veronica alters the squad's course to her destination, and right as the flag ship jumps, one of the HEVs crashes into your own. You awake hours later inside your HEV, and you must press a few buttons to eject the door. Once done, you drop an incredible height and lose quite a bit of stamina and health. Yes, health is back, and plays an important role in your survival. Your stamina acts as a "shield" of sorts, as you can't lose health without first losing your stamina.
You end up walking around the darkened city, either eliminating or evading the Covenant patrols, and eventually get a notice to link up with the SuperIntendent, the city's AI. Once you do, the kind friend hooks you up with a map, and once you hit the back button, you realize just how large this city is.
The basic gist of the game is to find out what happened to your squad, and you do this by arriving at beacons, inspecting objects, and going into a CSI moment where you piece together what happened to the particular squad member you're reminded of. This puts you in the shoes of every person in the squad at least once.
The gameplay has changed from the other Halo games, in that you don't feel like a super soldier any more, and Bungie does an excellent job showing you that. When you jump, your character will grunt at times, and your head bobs a lot more when you walk or run. You'll also quickly find out that you cannot run-and-gun in this game on your own. If you have three other players though and can coordinate attacks on the fly, then you're in good shape.
The game adds no multiplayer for ODSTs, except for the Firefight mode, which is a four player co-operative mode where you take on waves of Covenant troops, much like many survival modes. This one, however, is the first survival mode where I haven't gotten bored of it. It really keeps up the pace by adding in different kinds of soldiers to attack depending on the situation of your soldiers. Me and my friends were doing so good that the game decided to send us four brute chieftains. We weren't happy.
There's not really much else to say, except that it is indeed an excellent game, even with the short campaign, which I will be playing over and over anyway. If you're a Halo fan, and love the lore, this game will be great for you. If you're a Halo fan and don't know much, check it out anyway, and you may like it. Hell, I know non-Halo fans who are really liking this game.