Far Cry 3's ending wasn't really awful. If anything, it's probably got the most positive ending in the series. The bad ending is bad, but considering what you do to get it you'd kind of expect something like that. Even aside from that, the endings in the Far Cry games (aside from FC1, which was basically Crysis 0) generally lean towards bittersweet, not horrid.
FC4 is probably the most derivative. It was pretty much a reskinned 3 and actually took features out of the base game (and replaced it really fucking annoying shit, like hawks randomly attacking you and forcing you into a QTE). FC4 is what I played the least, by far.
FC5 has a lot of nice little QOL features, and it doesn't really feel like the previous open world style games. I mean, the core mechanics are obviously similar, but things unravel in a far more organic way. Instead of getting a populated map by doing simple, monotonous tasks, you have to actually explore the world and talk to people. You don't reveal the map by climbing an annoying radio tower, you reveal it by walking around and talking to people. So I guess in that regard it's probably one of the larger refinements to the series since FC2 gave way to FC3.
As far as QOL improvements go, crafting is a much smaller part of the game. You don't have to find 3 bear butts to get more weapons anymore--you get it through perks. Hunting is literally only there to make money and to get some extra perk points.
The weapon balance is kind of all over the place. The gun nerd in me is driven crazy when they do really silly things like give the .45 ACP cartridge more power and penetration than a 5.56 NATO round. Then again, that's not something that's new with FC5, it's just something that they never addressed. Still annoys me, though!
Really, my main gripes with the game are with about half of the story. You can tell that the area that they steer you towards at the beginning is the one that they spend the most time on. The other two areas are kind of all over the place, and the ending made me legitimately angry. If you haven't seen much of it, I'd say it's worth the journey, but the ending just hit me in the exact same way that ME3 did, and it had the exact same effect: it made me never want to play the campaign again because it all winds up being a waste of time in the long run.
It's a weird paradox. I would say that it's worth playing, but I won't play it again. YMMV, of course.
And again, that's all storyline crap. The gameplay is solid, and you can befriend a dog, a cougar and a goddamn grizzly bear and they'll WALK AROUND WITH YOU AND TEAR SHIT UP.