Saw might have a lot of gore, but it doesn't rely entirely on it. Don't even compare it to that shitfest that is Hostel, and certainly not the Hills Have Eyes. Yes, it's gross, but I think nowadays more people go see it for the plot twist/puzzle aspect of it rather than the gore. At least it's not the same story over and over again, the plots of each of them vary.
Though it's true none of them live up to the suspense factor of the first one, but as for me, I watch it to try and guess the end and come up with crazy theories as to what's gonna happen in the next one, like with Harry Potter. I know it sounds like a odd comparison, but to me, and to a lot of people I know who like it, both online and offline, the anticipation level is about the same and they like it mainly for that, not necessarily the gore. In fact I don't know anyone who watches it for gore.
I bet more than half the money Saw V makes won't be because of gore, but because of fans of the franchise who actually want to know what happens rather than see more gore.
There's also the creative trap designs that keep people interested, but most of them admire the traps themselves rather than the gore that happens in them. If that makes any sense, though I'm pretty sure you know what I'm getting at.
But Hostel? The Hills Have Eyes? Hell, even Friday the 13th is repetitve, I actually gave the first three a chance. and got bored by the same story every time, a bunch of people at a camp get killed by Jason, one person survives and beats him.
But anyway, one more reason I have high hopes of part 5 being better than 2-4 is because it's got a new director who's FAR better than that of 2-4. And, I saw a few preview clips and it looks like it's gonna live up to the first one. Of course I won't know for sure until Thursday night, but I'll post what I thought of it. And it won't be biased, because I'll say right now I actually hated most of Saw 4, found it to be really weak.
But as for zombie movies/supernatural horror being better, and what Sam said above... well, can't really argue, to each his own I guess. I think it's much more interesting when it's something that CAN happen, ever see Misery?