Altair's voice acting in Assassin's Creed totally took me out of the game the first time I played it. He spoke in such a monotonous, unemotional way that sounded so contrived with his attempts to speak in an archaic form, and he didn't pronounce his words clearly, so I couldn't understand a word he was saying. I get that he was supposed to be a serious assassin, but, instead, he just had no personality. They should have used Desmond's voice actor. He was great.
Or, for that matter, why couldn't Altair have a Middle Eastern accent like everyone else in the damn game? Their performances were excellent, and I could understand them all perfectly.