You'll get used to the way the game scares you after a few chapters or so. So play it yo, the game's pro
That's a bit hard to say, though I would personally say the first game is "scarier" than the second because the first had a more eerie loneliness/ambience than the second one. Also, the lack of a main character voice in the first game (the only time he made any noise was screaming in pain or horror) compared to the second put me a bit more in his shoes.
Still, the second game still got me wincing quite a bit at some grotesque imagery. It seems there are even more ways the main character can get brutalized or dismembered here than the original. Also, it's pretty easy to get overwhelmed in DS2. All it takes is a misplaced stasis attack, or an unseen necromorph hawking a paralyzing loogie in your direction.
The game seems to cater to those that weren't around for the first game, bringing back every weapon and every "common" enemy from the first game, as well as a prologue from the main menu to get people up to speed. Also, in-game, there are tutorial-like instances of relearning techniques from the first game.
Not sure about anyone else, but I found the second game much more easy to getting sidetracked screwing around with the Kinesis ability, seeing if I could do damage by throwing a Teddy Bear or recycle bin at an oncoming creature.
Also, I found the story of the game series pretty damn good. It was basically the driving point of the game for me. the second answers quite a bit of questions as well as resolving the very last scene of the first game. Heck, not to spoil much, but the second game doesn't end on quite the bleak not the first one did