I just happened to watch it today. I never played the game, but the premise was interesting. But, for me, unnecessary. The parts with Torquemada in Spain were cool, especially the escape from the "auto da fe." The martial arts were fun and well done. Yeah, there was a lot of wire work.
Afa the historical aspects, both the Templars and the Assassins (or actually the group with that name), were supposed to have been wiped out by their religious brethren. Both groups were threats because they became too powerful. However, there are plenty of legends claiming that both groups survived and went underground. It's a lot like the Freemason conspiracy theories ... except, of course, for the hashish. At any rate, pitting two ancient secret societies against each other for control of mankind works on its own as a premise. Um, that and making the good guys Muslims, if also genetically preconditioned killers.
"A man is rich when he has time and freewill. How he chooses to invest both will determine the return on his investment."