Well, Connor did initially set out because he wanted to protect his village and because he wanted revenge on what the templars did to them. Ezio was also vengeful, the only difference is he took his revenge right at the start of the game and didn't have it spread out like Connor.
With regards to the combat, it's still as easy as it used to be, but there is now actually some challenge attached. Enemies can actually kill you, and they can do so rather easily if you don't pay attention. In 2, Brotherhood and Revelations it was nearly impossible for enemies to kill you. I once literally got up in the middle of a fight in Brotherhood, went to go make a cup of coffee and then came back to finish the fight.