The Abstergo challenges in 4: Black Flag haven't been too bad... yet. Though I'll say the 100% syncs have a few exceptions which are nearly as bad as the "do not push oh [sic] shove anyone!" 100% sync challenge that was in AC3. One of the 100% on Sequence/Chapter 10 has you stealth the entire mission and then have to "Rope Swing Assassinate" the one target which doesn't want to sync up with Edward's rope-swing assassinate. So it took me like... two hours... to land that thing because Edward would overshoot even if you mashed X (or whatever on keyboard) to try to initiate the assassination from the rope-swing. It's like "really, Ubisoft? You couldn't playtest this?" I mean because with the checkpoint they give you, you have to redo the entire "kill the guards checkpoints" and then try to rope-swing again. So it adds like 2-5 minutes to what should be a 2 minute checkpoint but then you have to do it via stealth instead of rushing in which adds another minutes or two to traversal.
And 10 Sequences in and you still don't have the Rope Dart which 3: Liberation gives you in like... 4 of it's... 10? 12? 18? Sequences... 
I don't remember the AC4 missions ever being that bad, but then again they were a breath of fresh air compared to the complete amateur hour that was AC3's missions. I still remember this one sequence (7, I think?) where you had to run across the town that was getting bombarded without getting hit (RIDICULOUS TO ACTUALLY DO) and to top it off swim to two boats, air assassinate a grenadier and blow the two ships up without being spotted (nevermind that the ships were LOADED with guards). The latter part took me upwards to 2 hours before i finally got it down, and its been the most frustrating thing I've ever been asked to do in a video game.
Yeah, I had to look up a guide on that "rush through the front to your assassination target." That mission could've been
awesome in some regards if you didn't have to do the stupid "don't get hit" 100% sync. It's like Ubisoft went full distinguished mentally-challenged fellow after Ass Creed 2: Brotherhood introduced the 100% sync side-objectives to missions and made them completely unfair or bullshit with no playtesting just to make them "interesting."
Though 4 introduced a blow dart which lets you "berserk" guards and anyone else into doing something similar to the poison from the shadows, so... technically... if you hunt a lot of shark and whales to craft the bones into darts (or get lucky looting them on certain people) you can basically poison people from the shadows and be "total stealth" now kinda... sorta..
Introduced in 3:Liberations, actually. It was way more broken then too, you could fire the dart while hiding inside haystacks (without having to peek out) and "berserkeing" a guard with it basically meant he'd kill the guy standing closest to him with a 100% success rate., then take out other guards on his own before dying from the poison. I was pleasantly surprised to see it back in 4, even in a nerfed form.
You're right. I never used it though since as soon as you get the whip I abused that "glitch" where you whipped someone into coming into your fist for an auto takedown.

I dunno if they fixed that in the "HD remake" but that was so broken in the initial release.
I just finished Black Flag today after like 4 hours of straight playing, BTW. Story was worthwhile, I liked how it ended the conflict even if it dragged it out for a hell of a lot longer than it needed. I feel Edward should've became an assassin much much much earlier than he did. But the journey was worthwhile. As was the epilogue. Good to see he finally went home and became a family man, despite the bad end for his wife.

Doesn't show why Haytham went with the Templar's though. Guess we'll see that in Rouge, maybe... Probably not.
I dunno if I want to buy the DLC or Stand-alone version of Freedom Cry. I know I'll get around to it eventually (ugh) but I'm probably going to take these next few weeks/month break to decomp before doing Unity, provided the system requirements aren't a huge leap over AC4's. For the sake of the co-op before it dies, like Splinter Cell: Blacklist.

More catty dragging and shade though is going to be awesome, especially if it turns into meltdowns for the people who keep complaining about popgaf.
spoiler (click to show/hide)
Where's Awesom-O, pre-emptive

Pre-emptive? He's always mad, bb.
And if POP-GAF becomes POP-BORE, please have a basic lingo dictionary I can keep on my nightstand in the OP for reference purposes.