In Halo: ODST you're dropped into New Mombasa when a Covenant ship jumps into slip-space and alters your trajectory.
You wake up six hours later, separated from your squad. You release yourself from your drop pod and fall to the ground, noticing that the edges of your screen go red as your character struggles for air.
That's when you realize: you're just a human, not a Spartan. You're shorter, can't jump as high, and your shield is … not there. You do have your VISR mode: a night-vision in which you see the outlines of buildings, allies and enemies.
As you roam the city, you come across your first enemy. You've been here before, however, you're not new to killing Covenant Jackals and Brutes, so you rush in.
You're getting shot, but something odd is happening - you're actually getting hurt. Your vision's going red again and you have to find cover and hide.
You charge for a quick melee. You run up to a Brute Captain and have to look up to him. When you melee him, he shrugs it off and hits you back, depleting your stamina and your health bar.
There's an obnoxious beeping noise reminding you of this damage, so you take cover again and wait for your health to regenerate. But you forgot again - you're not a Spartan anymore, you don't have a shield and now, you need health packs if you want to get back to full health.
You are going to have to put aside your pride and realize that if you don't find cover, you're going to die; if you rush in, you're going to get hurt, and when you're hurt, you're going to need to find health packs. You can't deploy items anymore, you have no shield, and you can't jump from buildings without hurting yourself.
You have your VISR mode, however, which makes nighttime missions a bit less threatening, a game with a more open world feel and a Superintendent to help you solve the mystery and find your squad. You also have two new guns: the Silenced SMG and the Silenced Magnum (the latter meant to replace the now-absent Battle Rifle for headshots).
On top of that, you have the new Firefight mode, similar to the Horde mode in Gears of War 2, where you (whether alone or with friends for cooperative play both online and off) face wave upon wave of enemies that increase in intensity and difficulty the longer you survive.
Play begins with one skull on, which places a new level of difficulty on game play (for example, having the enemies throw more grenades), and then adds one every time you survive a round, adding a new aspect on top of the last.
You also get a Halo: ODST multiplayer disc with all of the map packs, including three new ones, and the complete multiplayer experience. This is not your average Halo game, and despite being billed as such, it's a whole different perspective on the United Nations Space Command's run-in with the Covenant.