A great game with many things done right. Very enjoyable if you can get past the flaws.
Assassin's Creed overall has great graphics. There are a few graphical glitches here and there as well as some slowdowns, especially when the camera pans out at viewpoints, but they are hardly noticeable and do not affect gameplay. Assassin's Creed has plenty of graphical detail in everything and the draw distance in the game is very impressive.
Audio –
The music and sound effects in Assassin's Creed are average. Voice acting in Assassin's Creed is where they do a really great job. Besides the fact that 99% of the people in the game speak English, it is believable that you are going through cities during the time period of the Crusades. The dialog and the accents of each character fit nicely. The only thing I don't understand is how badly they messed up on Altair's voice acting. Since everyone else's voice acting is so great, Altair's plain American English sounds terrible. It stopped me from being truly engaged in the dialog at times. Overall, it wasn't that big of a deal to me, but it may truly annoy others.
Gameplay –
Even though AC is considered a "sandbox" game, there aren't that many objectives once you're inside a city. You can 1) Climb buildings and reach view points, 2) Rescue a citizen, 3) Beat someone for information (or just for fun), 4) Eavesdrop, 5) Pickpocket, 6) Collect Flags, 7) ASSASSINATE! Everything feels really repetitive, including fighting. Still, each individual part is very well done. Climbing buildings feels very natural and fluid. The player can easily recognize what can and can't be climbed, and nothing looks out of place. Controls can feel a bit non-respondent at times when climbing (especially when you are in a rush trying to escape from guards!), but if you are patient, Altair will climb it. I really enjoyed scoping out the layout of the buildings/rooftops to find the best route from point A to point B, and then executing the route as quickly as possible. Fight sequences were very fun as well. You can just button mash the square button to have Altair attack whatever he's targeting, but later in the game you will see that enemies will guard and counter more often. As you progress through the game, you obtain new weapons and abilities to aid you in fights. The abilities are used by timing attacks and parries, resulting in some very SWEET action kills that feel very rewarding. Assassinations can be executed in several different ways, so it's always good to plan the assassination as well as think of an escape route. Assassinations are always very dramatic and feels rewarding as well, especially when you kill your mark without alerting any guards.
Conclusion –
I had read reviews about the game and had been warned about the repetition. After the first two assassinations, I wondered how much longer it would be before I got bored from the repetition, but to my surprise I never got bored and had a lot of fun finishing the game. There are some parts that are bad/annoying (e.g. Altair's voice acting, can't skip mission briefings after you fail, Altair can't swim so if you fall in water you die, poor AI sometimes), but nothing really I couldn't get past. This game may not be for everyone, but I really recommend that if you are interesting in the game then rent/borrow it, play the first 2-3 missions, and if you're still interesting then buy it.