I can't hate on a horror series for going on too long because I'm a huge Nightmare and Friday fan. But I stopped caring about Saw after 3. I honestly don't remember the third at all to tell you the truth. I re-watched the first 2 after not having seen them in a long while and I forgot how good they were. The first one in particular is still one hell of a good horror movie. I remember being blown away in the theater when it first came out. The second one almost matched it in the intensity department.
One of these days I'll probably catch up with the whole series, but it's not high on my list.