Approach this game as if it is Grand Theft Auto in Jerusalim and you will enjoy it immensely!
Now let's see what's missing in this game!
There are four different cities in the game that are the best settlement representations I have seen in a virtual world. They look even more alive than Liberty City or San Andreas. However, you can do exactly the same things in all four of them, you enter each one of them exactly the same way and citizens in them speak the same four lines all the time.
The goal of the game is to perform 9 assassinations and each one of them is specific, intense and interesting. However, in order to get started with the assassination, you have to reach the city, free a citizen that is harassed by thugs at the gate, scholars appear from nowhere, you blend with them and walk past the guards. Once in the city, you jump on the nearest roof, look for a higher tower, climb it and observe the area, revealing part of the map. After that, all the points of interest in your vicinity pop-up on the mini map. You air-dive from the top of the tower in a conveniently placed cart full of hay underneath then proceed to the nearest mission. You do all this in exactly the same order every time you set on an assassination.
Each assassination has six investigation missions affiliated with it. Depending on how far in the game you are and what difficulty you are playing at, you have to complete a certain number of these investigation missions in order to be allowed to do the assassination. The drama here is that there are few types of investigation missions and they repeat far too often. You either have to:
1) Run from one point to another within given time limit;
2) Escort a fellow assassin to somewhere;
3) Break merchant stands;
4) Collect flags;
5) Assassinate archers on the roofs;
6) Assassinate thugs on the streets;
7) Eavesdrop on a conversation;
8) Rob someone;
9) Interrogate someone by beating him senseless.
I might be missing a type of mission or two, but as you can see, diversity is limited, especially if you decide to do all missions to unlock all memories. (If you actually decide on that, mind that many of the thug killing missions are pretty much impossible, because you have to kill the targets silently without alarming anyone, but they tend to circle densely populated city squares with lots of guards nearby. Throw in a time limit to that and you risk lots of nerves in completing that.)
Another problem with investigation missions is that they are often given by the same indistinguishable NPC and don't make any sense to the main story. While this is OK with side missions, it is unacceptable with what drives the story forward.
Speaking of side missions, there are interesting, yet again few other things that you can do apart from working towards the assassinations. You can collect the abovementioned hidden flags though they are so numerous, I don't believe many people will have the nerve for that. You can also kill special Templars who, again, are placed on hidden spots. Each area that you enter has view points that you can climb and they count and in cities, there are people to be saved from thugs. And that's it!
All of the above is interesting, yet it makes the game more appealing to gamers who would spend 20+ hours looking for the 98th hidden package in GTA rather than those who like to unravel mysteries.
Now for the award-winning parts that everyone should like. Graphics are spectacular. A lot of modern games look great but this one deserves special attention. As I said, cities look alive. They are dusty and noisy, too and there is a nice colour filter used that makes everything look even more authentic. Camera work is well done like in a movie, especially in key moments. Altair is agile, but he looks entirely human unlike some of his comrades-by-genre.
Combat deserves merit as well. It is smooth and spectacular and counts on correct timing rather than memorizing insane combinations of buttons. Weapons are heavy and sword swings and clushesh feel heavy on the hands. Motion capture is done perfect. The only problem that undermines the impression a bit is minor clipping issues like parts of clothing getting through limbs, etc. AI is also a bit dumb and guards often do not pay attention to your aggressive behaviour. Furthermore, you can often hide in a lonely hiding spot and guards will start circling it but will never find you and then the moment your indicator says that it is safe to walk in the open again, you can pop right out, bumping into still wandering guards who apparently have suffered an instant memory loss and will disregard you altogether.
Another likable feature of the game is its story and the whole setting. The Promised Land keeps many secrets and it is one of the places on Earth where history and mythology blend the most. It holds huge potential for telling exotic stories and Assassin's Creed is one of them though, as it became obvious from announcing the game as a trilogy and the flat ending, we will have to wait for two more games to reveal the whole of it.
The Hashshashin faction to which Altair belongs and which is the origin of the word "assassin" is one of the more interesting bits of the history of mankind which inspires the imagination a lot. Check the internet for more info on this order. It is well worth it!
There is just one thing of the story that I didn't like. It is a bit of a spoiler, but everyone has been discussing it since the game came out and it is in half the major reviews on the net so I am not ruining anything here - the action in Assassin's Creed takes place not in the past but rather in the future and what you play are actually the memories of a far descendant of Altair caught in some funky machinery. When you are in the middle ages, everything is fine, but there are also some small bits of gameplay in a room with the memory device which are badly stitched to the other features of the game and would have been far better if left like non-interactive cut-scenes.
All in all, Assassin's Creed is a very good game that falls short to what was promised in the beginning, but I don't remember it anymore, so I enjoyed the game a lot :).