Well, FC3 was fun and since FC4 is more of the same, it is also fun. This thread pushed me to start FC4 since it's been sitting in my library for a very long time and it's a blast. I don't really like how the paths are pretty black and white and I'm sure it will give you a similar choice as you had in FC3, but the world is big enough that I'm finding plenty to do and the outposts are actually fun to do this time around.
My only gripe with the game is how easy it is to unlock pretty much everything right out of the gates. Almost all the craftables are available right from the start, but most guns are locked for way too long. As in, you get both bows right off the bat, but I'm 60% through the main game and still haven't unlocked the crossbow yet... doesn't make much sense. And the requirement of getting Rank 10 in the arena is a bit silly since it's just non-stop grinding. It would be different if the arena battles changed, but they don't. They should have taken a page from Borderland 2's book about arena fights. I think I'm rank 6 and I really don't want to continue just for that signature.
All in all, I still don't understand why people have to try to be critics about everything. Video games are meant to be fun, not judged based on how realistic the facial expressions are or if the game reuses animations from previous games. If it's fun, then play it. If you don't find it fun, move on to something else.