Lee, or El Duderino, if, you're not into the whole brevity thing’s review published on Letterboxd:
"Game over." *SLAM*
Still by far the best in the franchise, because it's actually its own independent narrative that can stand alone as a serial killer cop thriller. I do wish we had gotten more time with the Danny Glover cop procedural investigations à la 99p Se7en, because the second act's bouncing around gets a bit dull, especially on rewatch. Saw excels when it functions in its locked-room thriller setting, but I do applaud the additional successful foundations set here for the unexpected explosively popular franchise to come; crumbs are laid here for things only revealed 6-7 films later. As a mainstream feature debut, James Wan and Leigh Whannell really and literally proved their guts here—essentially locking them in as the then next horror names to keep tabs on. It's key to remember that this was very low budget for these first time Hollywood greenhorns—hence all the frenetic and...spiral movement to conceal and distract. I do think a large part of this film's success and legacy spawned from the ridiculous word of mouth and the false obsessive tendency to be labeled "torture porn" by the media. Having recently gone through the franchise again since release (just needing to cap off the first two out of order due to scheduling), the gore doesn't really ever get too excessive; the trap kills in the first are extremely minimal and even avoid showing most of the gore and aftermath (maybe budgetary rational). If anything, I'm curious if the reason the gore got more gruesome and extensive down the line is because that's what audiences wanted more of...and larger budgets allotted for it. Key to remember Saw was made for $1.2M, Saw II got $4M, III got $10M, and I'll comfortably estimate Spiral getting ~$20-30M; each film would typically always make over ten times its initial budget at the box office as well.
Unnecessary moniker aside, the other element this film really had going for it was a great off the chain Cary Elwes—who had been practically MIA since 1997's Liar Liar—career revival performance, and that epic ending reveal. I still recall seeing it in theatres as a kid with my dad, then being able to brag about having had seen it when brought up within school convos. Those final ~6min still slap hard, especially with that iconic former NIN-member composed theme kicking in: it's one of the few modern original musical themes that have a well established place in my mind. You know exactly what it is when it begins, and you already know that I keep it whistling days later.
PS: For what I believe is a second lead role, Leigh Whannell could have done far worse acting wise. I'm actually a fan of his select few acting efforts.