Hard Vacuum
The demo began in the early portion of the game, when Isaac is just beginning to realize that his mission to fix a damaged communications rig on a ship called the Ishimura is going to require massive amounts of hazard pay. Using his magnetic boots to navigate portions of the ship that have been exposed to the nothingness of space, Isaac must re-enter the ship via airlock or risk running out of precious oxygen (presented in Dead Space's standard HUD-less display system as floating holographic numerals on Isaac's back). Outside the ship, however, the combination of floating debris and damaged portions of the ship venting gases and liquids into the deep chill of space was hauntingly beautiful, threatening like sirens to captivate us long enough to lead to certain doom.
Of course, our trip across the exterior of the Ishimura was short-lived, as Isaac was able to locate an entry point soon enough. But while that brought him back into normalized atmosphere, there was still a distinct lack of gravity. In order to restore gravity, Isaac must restore power to the ship's generators by plugging boxy contraptions into similarly boxy contraption-shaped holes. He does this by plucking the boxes out of the surrounding environment using a Kinesis Module, which enables you to use telekinetic abilities by pressing the B button (Circle on PS3). As you might expect, once Isaac has restored power to the ship, things that were previously suspended suddenly crash to the floor around Isaac... it isn't dangerous, but the effect is still pretty shocking (and totally appropriate given the scary nature of this game).
Shoot the Legs, Johnny
Combat consists mostly of ranged attacks, but Isaac does have the option of smacking things around melee-style (pressing the right trigger accomplishes this). This is not advisable in most situations though, because the enemies that you face mostly look like the spawn of the alien from John Carpenter's "The Thing," right down to an inordinate supply of wriggling tendrils sprouting from inappropriate places on their bodies... generally not things you want anywhere near you.
Instead, Dead Space requires you to use an approach the developers refer to as "strategic dismemberment." Unlike most shooters where the ultimate test of skill is the venerable headshot, Isaac's foes don't rely on brainpower particularly heavily, so destroying an alien's skull (or what appears to be its skull) doesn't necessarily have the desired effect of crippling the monster. In most cases, scoring a critical headshot will result in the alien literally losing its mind and going into a berserker rage, lashing out in every direction with as much ferocity as possible.
In order to effectively deal with the ravening hordes, Isaac is encouraged to aim for limbs, tentacles or flexing trunks... anything that can hobble the alien and limit its mobility is ideal. The outcome of this tactic is almost inevitably a disgusting and bloody writhing pile of viscera, but Isaac also gets to keep his spinal cord, so as long as you aren't squeamish, it's win-win.
In practice, Dead Space appears to be hitting the right notes in terms of striking a balance between tense build-up moments and gruesomely bloody payoffs. Totally appropriately, the game is slated for release this Halloween.
