Um…FC4’s story and characters are definitely better. FC3’s protagonist is a bit of a douche.
The gameplay was more polished in FC4. FC3 invented the mechanics, FC4 perfected them. So they play very similarly with hunting and crafting and side missions and exploration and such, it’s just FC4 felt more immersive to me.
What FC3 offers is that island vibe. You start on a big island, and soon get access to a 2nd smaller one, and you spend your first 2 dozen hours or so exploring and fighting and it’s great–but a 3rd island that’s about 40% of the total map size you don’t get to visit until you’re close to the end of the game and pacing-wise it’s awful.
You’ve been doing all this stuff, taking outposts, pushing back the enemy, and with like 2 main story missions left there’s a big new island with at least half a dozen more outposts and tons of things to do…it felt like I just got reset to the beginning of the game! It was a slog to get through it at that point.
I forget how many hours it took me to finish it, but I would say the first 3/4 of the game was a delight but the last 1/4 really made me weary. FC4 instead opens up gradually and more naturally, pacing is much superior.
I put over 100 hrs into FC4 thanks to coop and the DLCs. I didn’t even put half that much into FC3 even with the handful of dedicated coop maps (unlike FC4 where coop is the main story, and only a few side missions are exempt from coop).
I’ve played FC1 and 2 about 4 times each because they’re paced well and good fun, even if the mutants at FC1’s end can be trying. I would like to replay FC4 some day, but I don’t know about FC3. Once might be enough.
That’s my take FWIW–if you really liked FC4, I think FC3 is worth getting on sale for a single run through. It’s not as good as FC4, though, no.