The worst part of being at the movie was that some woman brought her little girls (who were under 10 years old) to it. Like a couple of children really should see any movie of the "torture porn" genre. Of course, there are worse parents out there, but are you kidding?
About the movie in general, though, I agree with some of the critics that pointed out 1) the poor acting, and 2) some of the inherent gaps of logic.
I was looking forward to seeing Scott Patterson as Straum, but was disappointed with how he played the character. I thought that he played it far too aggressively. The anger and frustration in his performance seemed a little out of place for a character who, I assume, would have dealt with murderers (serial or otherwise) prior and did not have any prior history with the case (other than contact with Kerry's character). Granted, I can understand that any individual would be frustrated with the fact that Jigsaw, by this point, seems to demonstrate precognitive abilities.
Related to some of the other poor acting, some of the dialogue was over-the-top and out of place, particularly the profanity. For the most part, I only have a real problem with profanity when it seems unnatural on the part of the actor and the character. There were a number of times in this movie that it was poorly performed and/or written.
I was satisfied with Lyriq Bent's performance, though there were aspects in which he was not written well: Primarily, at the location of the "Feel What I Feel" test, a photograph of his wife was left and, written on the back, it said "She needs you." Given that Rigg's test was about his "obsession" with saving people, you would think that he would go check on his wife to make sure that she was okay or, at the very least, call her to make sure that she did not need saving. One could argue that he did call her between scenes, but it wasn't in anyway implied. One could make a second argument that he thought she was in a trap as well, but this wasn't implied either.
Furthermore, I don't believe that Rigg's character, a character who is obsessed with saving people, would put someone into one of Jigsaw's traps, even knowing that that individual was a rapist. It is one thing for people to say that such a person might "deserve" it, but it is completely another to actually do it. This is even more ridiculous since Rigg 1) wants to save people (his obsession), 2) of course, wants to actually stop Jigsaw, and 3) did not need to put Ivan into the trap in order to get the clue to the next location (unless I am recalling incorrectly). And let's not forget that, at the "See What I See" test, Rigg put forth the attempt to save a woman who was prostituting children.
As far as the traps go, I am very glad that none of them were as graphic as the "Rack" trap in the third movie.
Overall, it was definitely not as good as the first or second installments as far as the general creativity of the plot itself. Though the third movie arguably had better performances than Saw IV, I consider IV to be better than III on account of liking the primary character (Rigg). Though Angus MacFayden's performance was fine, I hated the character he played.
(And there are my unorganized thoughts about Saw IV.)