I loved Dead Space 1. Beat it three times, the third time on Impossible with just the plasma cutter. Wicked fun.
Dead Space 2 was okay. Played through it once and never had any urge to go back to it. But like I said, I didn't pay for Dead Space 3 so there was no reason not to play it. Well, now I have a reason not to play it, because it's total balls, but if you're "not sure why I bothered with Dead Space 3," it's because it was free.
I'm more curious why you think it's total balls? I love Dead Space, DS1 being my favorite PS3/360 game. I'm finding DS3 to be extremely enjoyable.