Dead Space is a nonstop, balls to the wall, sci fi treat.
Gameplay- Dead Space does away with the headshot kill mechanic and forces you to kill your enemies by dismembering them limb by limb. It's a refreshing change.
The weapons are unique in the fact that they have practical uses in the futuristic sci fi world. No more rocket launchers and sniper rifles. The weapons are awesome though and provide different strategies provided what enemy you are facing.
The big change in DS that sets it apart is Zero G gameplay. Some parts in the game have you solving puzzles and fighting enemies in a zero gravity vacuum. You and your enemies will jump dozens of feet from wall to wall fighting in zero g. It's a refreshingly unique gameplay point.
Graphics/sound- Both shine. The graphics are perfet for this game. There are some sci fi planet visual treats, along with some grotesque aliens, mutilated bodies, crazy bosses, etc etc etc. The audio is superb as well. The score keeps the tension flowing throughout the entire game. The monster sounds and weapons effects are done extremely well. The voice cast, although limited, is done extremely well.
Fun/Value- This game is incredibly fun. One of the best and unique gaming experiences I've had in the last year or two. It's about 8-11 hours long, but there is a lot of incentive to play it again.
In summary, if you like horror games, or just like well designed, brutally violent shooters with an awesome, deep story, Dead Space is for you