Saw 6 is the last one, definitely. After 3 came out they said they were gonna do 4, 5 & 6 and that was it. Whatever, 6 better be better than 5 or else why even bother?? OK, 5 wasn't totally devoid of any good scenes, but they couldn't make the story interesting or make us care about, well, anything that was happening in it. There was no real big twist at the end, which at this stage is pretty unforgivable. The last one should have the biggest twist ever to compensate.
Sadly, the spirit of the first Saw is all but gone. Didn't they shoot Saw in 12 days, or something crazy like that? And there was only one exterior shot which they shot illegally without a film permit!