They ruined Jigsaw for me. He's a villain, I don't want him too likable. They already gave a backstory for why he's doing all this in Saw 1. The guy went through a near death experience with cancer and when he survived, he saw so many people taking for granted what he, for a time, didn't have. The whole tagline of the series "How much blood would you shed to stay alive?" plays right into that.
That in essence is a prime example of the problem of the series. They kept trying to add new twists to explain things that had already been explained, solely to keep the series going. Everything you needed to know about John was answered in the first movie.
Why did he do this? Anger in how people treat their lives while he was on the losing battle of his own.
How did he do all of this when he was so weak? Had Zep's help
That's it. That's all you needed to know. But then they added in the additional help of Amanda. But wait, he secretly had Hoffman there to help too. Lawrence died, wait...no, he survived and randomly decided to start helping Jigsaw. Jigsaw kills because he had cancer. WAIT...he really began because his wife had a miscarriage. Oh, but now he's doing it because he just likes convincing people to cherish their lives. Hoffman just loves to kill. So Matthews died, oh wait, they decided to let him live so his Rigg can accidentally kill him in Saw 4. Rigg was put through the tests because he cared about people too much. Wait...wut?
The whole series became so convoluted with character's motivations changing, new twists that don't really make any logical sense and a progression of lead heroes meaning less and less.