Fall of Rome was probably the most interesting way you could go for a total war no diplomacy scenario. Plenty of sides, varying approaches, and most importantly, the prospect of the Roman Empires getting negative social policies, sending them further into decay. That made the Roman angle very interesting, having to fight a nigh-unwinnable defensive game while things just get worse and worse and worse for you, especially for Western Rome where you don't get the nice Fort bonuses. The four west-oriented barbarian groups weren't all that amazingly interesting, they were kinda plain war-focused civs with one in the water and all that, but the Huns were a blast, you can wreck things so hard while everyone else scrambles to get anything together. And the Sassanids were just if you wanted to play it like a more normal game, aiming for continued prosperity and expansion, with the might to back it up. There's a lot of ways to play it, since your goal is basically "welp time to take whatever I want!".
ACW by contrast is very simplistic. There's only one way you really can go, up or down, only two sides, and the goal is a straightforward "take the capital!!!111!!". The map is just...a coastline, no interesting features giving some strategic importance aside from a river and a bridge over it, and the setting isn't as enticing. Union vs. Confederacy, yawn, I learned about this eight times in grade school. Gimme something more esoteric and interesting than somewhat lopsided infighting. The prospect of the mighty eternal center of civilization crumbling and anxious tribes leaping at the opportunities arising from that is much more enticing than some overly bloody squabble over slavery and/or states rights.
The Africa scenario is gratefully really cool and fun to play more than once. I do love scenarios that give you incentive to try them more than once, and this definitely delivers. It's all the ambition and hugeness of the Renaissance scenario combined with the exploration and intrigue and themes and replayability of the New World one. It feels less like simulating some isolated incident and more like immersing yourself in a world where the stage is set and this part of history is your oyster, ready to be shaped and molded into a wholly realized chunk of the world for you to grasp and fight to come out on top of.