Going decent so far. Side-quests are similar to Far Cry 3. There's a choice factor implemented into it now which is a nice touch also. The co-op has been introduced well - I think I'll try that out after my first play through. Kind of don't want to give out too many details though so as to spoil it for you guys haha.
There are several more interesting locations to explore than in Far Cry 3 giving it a more realistic feel than rather there being a few abandoned buildings and just outposts/towers. You can grapple onto things with a grappling hook and get a wing suit which both allow for some interesting exploring opportunities. I'm so terrible with the wing suit though haha. Driving can be a little bit sluggish but that's more nitpicking, the auto-drive is a nice feature though. Raised my outlook to a solid 8.5-9.