I'm a few hours in and enjoying it so far. The early game hews so closely to Far Cry 3 that it almost feels like a reskin rather than a sequel, but as you get further in, new options open up for you.
Took my first outpost by sniping the alarm box, sneaking down and mounting an elephant, then trampling and tossing everyone inside. That was pretty funny. Hunting predators from the back of an elephant is also fun, though a bit one-sided.
I like the idea of the grappling hook, and the rope swinging you can do with it is pretty neat, but first person doesn't really lend itself to pendular platforming, so I've whiffed quite a few times.
I like the mini-copters. Kind of a necessary addition given the verticality of Kyrat. I witnessed my funniest moment so far from a chopper -- a rhino chasing a guy down, knocking him over repeatedly, and then head-butting him off a very tall cliff.
The game is very pretty. No framerate dips or hitches for me so far. HDR is a bit excessive at times, but cranking up the brightness beyond the recommended level helps a lot.
Haven't tried any multiplayer yet, but I'll give it a whirl once I'm further along.