Hah! What a question! As you can see, and as I noted, this will likely be something of a marmite film (who knows, maybe everybody but me will like it, but a few reviews I've read since have picked up on the final act) and so placing it in Fincher's film history is tough.
My personal fave is The Game, but Seven is so close it might as well be its equal at the top. As I mentioned, the first two thirds of this film gets us up to the giddy heights of The Game in stature, IMO. Those happy with the resolve will likely find it just as good, as a result, but those who didn't get on with the last half hour - like me - will never rate it amidst Fincher's best.
Indeed I'm struggling to think of a reason why I would watch it again... TBH, I felt the same way about Dragon Tattoo, but at least I could understand that people who hadn't seen the original would enjoy the remake. Here, there's no such justification.
The fact that so many people think it's a masterpiece means you definitely need to see it, but I'd be interested to know if anybody actually felt the same frustrations as me.
Cas