The American frontier isn't the problem. The problem was the story was hugely rushed, the game was bugged (to where 100% syncs at time were impossible) and the ending was so damn stupid.
Haha, I'd forgotten about the ending. I feel for anybody who was expecting an even remotely satisfying payoff after five games of narrative build-up (well, 4 if you consider that virtually nothing happened in Revelations).
AC3 also tried to reinvent a lot of shit that the Ezio trilogy had already nailed down to a science. Like, they made it so viewpoint synchronization wouldn't reveal the entire map, but you'd still have to physically wander around to fill out empty spots in it, sometimes revealing stuff that you'd 100% miss otherwise cause the game doesn't even lightly hint that its there. The fuck is the point of having the viewpoints at all then?
The worst thing about the viewpoint change is that there's an Abstergo challenge or whatever to reveal something like 80% of the map in each area, which means that, if you're aiming to 100% the game, after doing all the viewpoints you have to run around aimlessly for about 20 minutes. Top stuff there, Ubi.