First, let me say that Saw is a brilliant film. If you already know the twists, however, then don't bother. Any twist-laden film will be crap if you already know what is going to happen!
Subsequent sequels got progressively worse, as they became less about these twists and more about standard horror fare. The second one was OK, the third one was rubbish. Actually, the fourth one was quite good but it was annoying because it became obvious that the makers had long since given up on the idea of telling a particularly story in several parts (which the first two seemed to be doing) and had just started churning out an endless moneyspinner.
If you don't like that kind of film then fine, but you can't fault the first Saw, in particular, for the strength of its story.
Now -- Hostel, of which I saw about an hour last night. The hour I saw had no discernable story. As a lover of horror films, I have to say that it really did seem to just be about gratuitous displays of violence and was pretty shit. In fact, the violent scenes were actually something of a relief from the even worse violence perpetuated on the viewer with that awful, awful script. So, crap.
And yet quite watchable crap, despite that. I enjoy nasty things on film, because I enjoy being scared by films, frankly. "Torture porn" is a clever phrase, yet horribly wrong. It isn't titillating. Porn is supposed to be about arousal and it most certainly isn't arousing! Unadulterated nastiness on film makes it all more visceral, which in turn raises the viewer's panic levels about what is happening and gives you more connection to the events, more desperation that it stop -- vital to the horror experience. It's also about verisimilitude. If you are creating a world of horror then leaving out the actual horror rather stops the experience in its tracks.
Just a few quick thoughts from someone that does actually like these films about why I like them, because I don't recognise at all some of what has been written in this thread as being concordant with my reality.