To be quite honest, the only thing Dead Space 2 has in common with the first is the gameplay mechanics IMO, other than that, the setting is completely changed. It's a lot darker, and lighting is reliant on aiming your weapon for the most part with the attached flashlight.
I can't really decide if I like the first or second more. Even though the Ishimura got repetitive after awhile, I kinda miss the space station feeling of the first game. The second game, while I enjoy all of the great detail and attention put to the environments (the daycare in particular), is way too damn dark for my tastes. Doesn't really add to the scare factor, so much as it serves more as a way to give me a headache, causing me to frequently take breaks. I AM liking the increase in necromorph ferocity though.
Oh, and the damn Stalkers. Even though I hate those fucking things, you have to applaud the work they put into their A.I.