I saw someone describing Dead Space 2 as Dead Space 1.5 because it does not add enough to be a whole new game in their opinion. Which might be true. The story takes place in a different location and moves the arcing plot forward but the mechanics and how the game generally works are the same indeed (if more polished),
One significant addition to the series is Isaac having voice-acting. And -- surprise, surprise -- it works perfectly fine, like I thought it would. He sounded a bit different than what I imagined at first but I got used to his voice eventually. I also noticed the camera seemed to be the listener and Isaac's voice was coming in front of it. You would think that the character would be the center even in third person games. Either it was a glitch or I got used to it, as it definitely stopped bothering me very fast.
I again stuck to the plasma cutter and line gun. The former has a slightly different appearance in DS2, but you can get the old design if the game finds a DS1 save from your machine. I like such continuity even if very minor. This time I had a handful of spare power nodes at the end of the game. That was probably due to the reduced number of upgrade nodes available (no kinesis module, for instance). I guess I could have tried a different weapon, especially since there is a respec option.
The RIG's air supply is greater in DS2 and air canisters are everywhere, effectively removing suspense from the vacuum sections. Zero gravity also works differently; you can freely float around with the aid of the suit's thrusters but you cannot attach to any even surface like previously -- only planes facing the same direction as the floor you started from are walkable. Not that you really need to attach to anything. I just found it puzzling.
I think that Dead Space 2 is a safe bet for anyone who liked the first game. You get all the same cool stuff but better and improved. And maybe some new things as well. I did not really like the new bypass mini-game they added, though -- it seemed a bit unnecessary. But they actually managed make more of it, as at one point you get jump-scared in the middle of the mini-game and you also have to bypass a door while being chased by the Hunter again later on.