Dead Space went for the jumpy, in-your-face scare, as opposed to the kind of fear in System Shock 2, which was slow and relentless. (Think about your first run-in with a maintenance bot in SS2, watching the condition of your pistol slowly deteriorate and your armor-piercing rounds disappear, and you'll know what I mean.) DS made very good use of sound, and it was very well done, but I'd definitely say no, it wasn't as scary as SS2. Although it depends on what sets you off, really.
What was missing from Dead Space, for me, was a sense of humanity, of people living basically normal lives that were completely ripped apart by what had happened aboard the Ishimura. SS2 took tiny portions of the crew's everyday life and laid them atop the horror on the Von Braun so skillfully that it was reflected, as Root of All Evil said, not on the character, but on the player.
For instance:
The midwives' aloof, sing-song promise that they'll "tear out your spine," and their deadpan claim that "they grow up so fast." The latter is especially chilling for me specifically because it's completely out of context, but you know that they're reaching for some remaining shred of their human past, so it works anyway. Also, the way they hum that demented metallic-sounding lullaby as they prowl the halls looking for you necessitates a quadruple Fruit of the Loom bypass, every time.
The various crew members who've been taken by the Many, who come after you saying "I'm...sorry," and "run!" as they blast away at you with their shotguns. They realize that they're all fucked up, but enough of their humanity remains to try to warn you to beat feet before it's too late.
The slow, inexorable gait of the maintenance and security bots, who come after you not because you're the enemy, but simply because you're an anomaly. A nuisance to be dealt with. Same thing goes for the robot butlers, who chatter away amiably enough right until they, you know, blow the hell up all over you.
In addition, there are dozens of audio logs in SS2 that chronicle the last days of several characters, some of whom you grow quite attached to over the course of the game until you find them splattered all over a closet or hanging quietly in their quarters because they lost hope and saw no other way out. SS2 did a great job of keeping you right there, consistently on the verge of losing hope, because it used very personal and sometimes heartbreaking methods to remind you that hope is futile against the Many.
I'd definitely recommend Dead Space, as it's one of the best games I've played this year, but don't expect to be particularly frightened if you thought SS2 was scary. I don't know about Thief 2 and Fatal Frame 2, but it's worth picking up, regardless of the fear factor.
