You play Isaac Clarke, an engineer on the USG Kellion, a ship who sets out to investigate the strange happenings on the USG Ishimura, a mining ship that has fallen on scary times. Unfortunately for Isaac, his girlfriend Nicole is stationed on the Ishimura, so he has a vested interest in finding her and getting them out alive. When your ride gets blown to smithereens, it looks like you and fellow crew members, Kendra Daniels and Zach Hammond, are stranded on the very dangerous Ishimura which is now crawling with Necromorphs, alien creatures that reanimate the dead passengers of the Ishimura. Confused? Rent or buy Dead Space: Downfall
for some backstory, which I highly recommend.
The HUD is somewhat unique. You can access it at the touch of a button and it pulls up all manner of helpful goodies such as your inventory, a map with important data like save points and stasis recharge stations, mission logs and your current objectives. You'll need quick and handy access to all of these things because when you are attacked, it'll be fast and furious. As you are exploring the ship and trying to craft your escape, enemies can pop out of air vents or arrive unexpectedly. You can be walking down a hall and a corpse can suddenly jump up and attack. Pre-emptive strikes are well advised.
Since you are trapped on a mining ship, it would make sense that your weapons would be things available on the ship. You start with a plasma cutter (like a light saber, but bigger!), but you will gain access to a line gun, a pulse rifle, a ripper, a contact beam, a force gun and a flamethrower. As you manuever around the ship, you can pick up health, ammo, credits, (which can be used to buy new weapons, ammo and health at The Store), schematics for new weapons and ammo, and power nodes, which can be used at The Bench to upgrade your weapons and your suit. Power nodes aren't that plentiful, so you need to be careful how you apply them and what you upgrade.
Probably the most important aspect of Dead Space's combat is selective dismemberment. When the Necromorphs attack with their sharp-bladed arms, you can use one of your weapons to take off a leg to render them unable to walk, then take off an arm so they can't scoot along the floor and continue to attack. If you don't act quickly, they will be on you faster than you can imagine. Sometimes when they do get the jump on you, you'll be force to rapidly tap the (X) button like in Resident Evil 4 or God of War.
Sometimes you'll run low on ammo, but never fear. You can always use your Kinesis ability. Take aim at an object and throw it at an enemy, or move something to make a path more accessible, even place a battery into a receptacle on the wall - the possibilities are endless. If you come to a place where things are all too crazy - enemies attacking too quickly or a door slamming back and forth - simply use your Stasis ability and slow things down a bit. Its all quite genius and provides for lots of different gameplay options.