I was on another forum where we were asked to rank our favorite Saw films in order ... and I'll simply post my response to the question ...
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I would have to break them up in terms of the actual plot of the movie, and then the actual surprise twist at the end of them. There have been some great Saw films that had somewhat of a letdown of a twist at the end. But there has also been some average films that had a phenomenal twist at the end.
In terms of twists at the end, I would rank them as follows in order of best to worst:
Saw 1
Saw 3
Saw 2
Saw 4
Saw 5.
I don't know if there's a soul out there that foresaw the body in the middle of the room being the actual Jigsaw killer, who played dead the entire time. My jaw dropped when he got up and revealed himself.
Saw 3 was the next best twist, in it that it was Amanda who was the actual one who was being tested. Never saw that one coming. Remarkable.
Saw 2, it was kind of obvious that Jigsaw wasn't acting alone, and I have to admit in all honesty I was very suspicious of Amanda the entire time. I just found it too convenient that she was placed in a trap for a second time. Plus, after discovering how the Saw franchise worked, with the movie being full of twists ... I wasn't surprised to learn she was the accomplice. However, I was surprised to see that the events of the second film were not taking place in real time, as the time when Matthews was talking to Jigsaw. That was a great twist.
Saw 4, again we knew there was an accomplice, and just like Amanda put herself in the trap in the second one, I knew that wasn't beyond the reach of the other accomplice doing the same in this one. One of the things that struck me earlier on, was that when Hoffman gets "captured", it never showed the person with the pig mask attacking him. It just showed the mask in the background. That was something I was surprised to have caught the first time I saw the film, and it stayed with me to the end of the film. So like Amanda, I really wasn't surprised to see Hoffman revealed as the second accomplice.
Saw 5 was the one twist I really wasn't all that impressed with. Straham was told to enter the box ... he didn't, and instead opted to put Hoffman in the box. What did we think was going to happen, when the instructions were clear that "if you wanted to survive the room, you had to enter the box"?
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So that's the twists.
Now, in terms of actual quality of the entire movies, the storyline, the complexity of the traps, the depths of character backgrounds, etc. I would rank them in this order ...
Saw 2
Saw 4
Saw 3
Saw 5
Saw 1
Like others have said, the House of Horrors in 2 was great, and the fact that you had a victim gone madman (Xavier) running around with the son of the cop that put him in prison, was nerve-racking. Also, the fact that there was a limited time, before they all died as a result of the gas. Then, while all this is going on, you have Jigsaw testing Eric Matthews patience to no end, while holding his son hostage. Great story. Great group of characters. I just wasn't impressed with Amanda being revealed as the Apprentice, as I figured it was her, anyway, earlier on.
Saw 4, again another great film, with a bit of a letdown (for me, anyway) on who the Accomplice was, as I was looking at Hoffman earlier on, since you never saw his actual capture on film. However, the whole storyline with trying to teach Rigg a lesson in that you can't save everyone was phenomenal. The fact that the whole idea of the film was that he WAS NOT supposed to reach Eric Matthews and Hoffman in 90 minutes, was another unique concept, that was pulled off splendidly. Great traps in this one, as well. The Hair Scalp trap, having the girl attack Rigg even after he freed her ... the domestic abuse victim attached to her husband ... and who could forget the serial rapist who had his eyes poked out with a spike, only to be dismembered at the end?
Saw 3, was again a good film, but not great. I liked the storyline of a man trying to go through a series of traps with the promise of finding his son's killer at the end. It had a good set of traps in it, as well. Actually, this film may have had the best set of traps. The woman freezing to death. The angel trap. The beginning where the man had to remove the key from his eye. But I found the acting to be a little wooden at times. I wasn't impressed with Angus MacFayden who played Jeff, and I was becoming annoyed with Amanda's character by this film.
Saw 1 was an average movie with an absolutely phenomenal plot twist at the end. That was why I rated this film to be the best in terms of plot twists, but everything else in the actual movie itself, I found to be average. I did appreciate the fact that they kept you guess on who the killer was. However, 85% of the movie takes place in the one room. The film still worked though, because it didn't come across as dragging, and the length of the film was about right. But again, it was the ending that made this film, and the franchise, what it is today.
Saw 5. I enjoyed all the Saw films, but thought this one had the least surprises, and the least interesting plot. It was all pretty much straight forward. We learned Hoffman's motives for why he did what he did, and how he got hooked up with Jigsaw. We learned the extent of his involvement, going all the way back to the very first Saw, and was helping Jigsaw since the franchise's inception. We know Straham is hot on his trail and is suspicious of him at the start of the film. So essentially we have a pretty straight forward game of cat and mouse between the two. I enjoyed the lesson of the 5 people being caught in the traps and the concept that they should have been working together in each one, but they really had no major consequence in the main plot of the film. They were just used as filler, basically, and a B Storyline, while Straham tracked down Hoffman.
So again, 1 takes the cake for best surprise. Where as 2, has the best overall storyline.