I thought it was pretty good.
They don't really focus on the horror much; by that point the necromorphs have kind of lost their shock value, so everyone pretty much treats them as annoying and disgusting obstacles.
And it does wrap up all those questions about the Markers pretty well.
If you're a Dead Space fan in general I'd say it's a good buy.
Well, this IS the internet. People like to be extremely impassioned about very petty things.
If you enjoyed the first two games, I don't see why you'd hate the third one.
Also, you get to fight a moon. Just putting that out there.
Well, then to answer your basic question: no it's not really that bad, and in fact I didn't find it bad at all.
If you like deeply psychological horror then you might find it tedious rather than thrilling; with a few brilliant exceptions, Dead Space doesn't do subtlety very well. Dead Space's idea of horror is having a talon-armed corpse stagger toward you, force you to dismember it, and then have the blasted thing grab your leg as you try to walk past its body after you think it's dead.
If you like that kind of visceral, violent horror, or just sci-fi shooters in general, then you'll like Dead Space.
I wouldn't recommend playing the games out of order, though. Especially not the third one. It was surprisingly story-focused.