Infinite free lives - that's what ruined it. You never feel any tension whatsoever because if you do get killed you'll just instantly pop back at full health in the nearest vita chamber.
I lost interest pretty quickly after realising this.
I don't think I've ever killed in it...even on Hard I think the only times I ever died is when I gibbed myself on my own trap bolts while I was killing a Big Daddy.
Only bad point for me about the game is it's very, very easy.