I understand how people who have seen the Saw movies can find them bad, because they are...for the most part. 
From the second movie onwards, the focus has been on elaborate and disgusting ways to make people mutilate and/or kill themselves or others. 

I don't know if everyone who hates these movies has seen the first one but there is little to no gore in it. 
In my opinion this makes it so much better because it is more of a psychological thriller rather than a "torture porn" type of film. 
It’s well acted and has many interesting twists that made it a great movie built around the emotions and mental state of the characters rather than shoving blood and guts in your face and then saying “oh, by the way there’s these people and stuff...” 
 
So my recommendation is see the first movie and never watch a Saw movie ever again.