[One of the problems with Assassin's Creed is that people don't understand it. We spend most of our time in CoD, Gears of War, Dead Space and Go-There-And-Shoot-Everyone. Assassin's Creed revolves around patience. A truly good assassin doesn't make a move until he's sure he can do it quietly. Gamers are too used to getting dropped into combat, handed a tool of destruction and cutting everything in half. Assassin's Creed I showed us that that's not how all games are played. It took forever to ride your horse to the next city, and another forever to hide, kill all the rooftop guards, gather information, stalk your target and knife him, but that's how it IS. It DOES take a long time to do that, and Assassin's Creed makes us sit down and do it RIGHT.
Games generally skip the boring parts and go right to the killing. In AC, you have to take your time and do it right. AC2 cut down on the time by providing fast-travel stations, but it still took a long time to find your informants, evade the guard, and stay in range of your target without him seeing you, but that's realistic. Granted, a good bit of it is unrealistic (the "war machines" in AC:B were way, way too over-the-top), but a lot of it is all about patience.
If you want it to be good, you have to sit and wait for one of the guards to break rank and then knife him. Open combat should be a last resort, although sometimes it isn't, and it never is in the ending section, but the rest of it is being careful and working slowly, and we don't like it because we're not used to it. We have to switch into a different gear. Yes, there are a lot of games out that make you run all over the place (Fallout and Oblivion come to mind), but every assassination target in Assassin's Creed 1 (minus the last one) was expected to be a stealth kill, then run and hide.
Personally, I got extremely frustrated with the series several times. It gets tedious and repetitive, but that's the only way to do it. As the series progressed, there were a lot more ways to kill a man (stab him and hide him, shoot him, poison him, push him off a roof or into water, etc), but it retained it's initial point: run out in the open, and you're going to get an arrow or two. Take your time and do it right.] this one deserve's a Merit