I've finished the game too, at 93% (I spent a lot
of time searching for GPS caches, treasure maps, and all the optional tombs. Then once I'd finished the story, I went back and finished upgrading weapons, and finding more of the challenges. I've not yet done all of them, but I'm up to 95% now.
I've had a blast playing the game. The bow is definitely
my favourite weapon as it's so much more accurate and stealthy than the guns. (That was the key to keeping the combat on my terms most of the time).
The timed events were okay - most only took two or three attempts, but the Russian guy was hard!
The optional tombs were fun, though I could have done with more.
The overall pacing of the game was fantastic - it builds to climactic scenes over and over again, but there are always times you can chill out and explore instead.
My overall impression is that I loved the open-world exploration stuff, and this is a game that's worth taking your time over!