Altair's adventures follow a set structure. There are three large sandbox style cities in the game, each divided into three districts which must gradually be unlocked. In each district you must complete a number of tasks in order to get enough information on your target to take them on in a variety of scenarios. The tasks required to gather information are all basically the same. You have to eavesdrop on people (simply sit on a bench and listen to them), interrogate people (follow them and beat them up), pickpocket people (pick their pockets unnoticed), collect some flags or assassinate some generic guards within a time limit. The game's main flaw is that it does become repetitive to do these tasks over and over, but I found it isn't a big downer on the experience as long as you take time out to explore (there are various achievements to be gained by doing so) and do the "save the citizen" side missions which result in some bloody sword fights. Once the information is collected you proceed to go to where your target is and after a cut scene you kill them, sometimes stealthily and sometimes in fully fledged bloody combat (depending on if they see you or not usually).
Combat in AC is one of the game's key strengths made all the more enjoyable by the game's fantastic controls. As you progress, lethal counter moves can be learned to slay even more guards and make you a killing machine to be feared by all if you get good at the timing of counter strikes and blocking. Altair can die fairly easily though evidently coming from the "made of jelly" school of male lead as opposed to the "built like a brick with a shot of adrenaline up its backside" Marcus Fenix side of things, so it's imperative to master all your weapons and skills quickly.
One of the finest achievements behind AC is the game's general look and animation. Never has a character moved so fluidly as Altair as he leaps from rooftop to rooftop, beam to beam with grace and realism. It's almost breathtaking to see him leap around animated so well, and I never thought I would say that about a video game's technical prowess. The visuals of the city itself look amazing too, with every building reachable, almost every wall scalable and every citizen on its streets reacting to your actions, begging for money, running in panic and occasionally slumping to the ground with a hidden blade in their eye. "It wasn't me Mr.Guard.. honest!"
To be honest with you, other than the repetition, there is little to fault Assassins Creed. It's lots of fun, has a good storyline and it's satisfyingly violent to shove swords in peoples necks. If you haven't tried it, it's well worth picking up now at a bargain price.