I may have rated Brotherhood too high and AC4 too low. I played Brotherhood right after AC2 so I was still riding that "best in the series" high. It probably isn't actually the 2nd-best.
Syndicate seems pretty disliked, but I love the setting. London is my 2nd-favorite city behind Paris, and the London setting of Syndicate is much more modern and fleshed-out than the Paris of Unity. You also finally get to play as a hot female assassin, something I wanted to see for ages. The visuals are just stunning everywhere you go. Yeah, I loved the hell out of Syndicate. The main downside to it for me was that the formula was super-stale at that point, being the final OG-formula AC game.
And I agree, fuck the assassins. We need more templar-based ACs. And one set in Japan. Nevermind, Ghost of Tsushima did that better than Ubisoft could, after years of the fans waiting for them to fill that niche. Ya snooze, ya lose.
After Valhalla is done, the only AC I'll have left to play is Chronicles. On one hand, the 2D ACs look kind of shite. On the other hand, their settings could be interesting. India, China, and Russia are places that haven't been touched-on like at all in the AC series. I just wish they were "normal" AC games, even scaled-down in scope, instead of weird side-scrollers.