User blog comment:SupremeAssassin/Assassin's Creed 3: Combat System/@comment-4530924-20120527214718
I've read it somewhere (sorry I can't source it) that there will be different archetypes, but this time around, they'll a bit more interesting. There will be the, for example, "Drum" archetype, which is just a dude with drums; seems harmless but if you don't kill him quickly then he'll call for back up.
As to how hard they will make the combat, I'd say that they should make it so you can only kill certain archetypes with certain weapons, like in ACII, when you can only counter-kill a brute when using the hidden blades. However, I'd like then to stir away from the cheap "you-can't-kill-one-hit" method they used in ACR with the janissaries. It slows the game down, makes combat a lot less fun and kinda turns a kick ass stealth-combat game into hack and slash.
I think that the tactics which must be employed to kill everyone effectively, chaining your kills together so that you're not only a killing machine but you look cool whilst doing it must be the real combat challenges in AC.