I personally thought AC1 was worst while looking back, just cause there's like nothing to do.
BUT, ACR was probably last/2nd to last for me.
I feel like they needed to add all these defense type games since Ezio was old and leader of the Assassins, so it made you play as if that's what he would do.
The loss of territory was a bit obnoxious too, but just keep your notoriety down and that shouldn't be an issue. It's tough when everything raises it so much, but between heralds and witnesses, and getting high level assassins to guard them, it isnt a big deal.
Ubisoft needed basically end this story line, so playing as 2 old assassins shouldn't have the same style as playing as young ones.
Even is ACR was the worst of the series, it was still super fun!