A game that's as fun as it is good, check it out!
Although you will kill a plethora of villains throughout the game, it is not really the focus. The game looks really beautiful and is fun to explore. This is amplified many fold by the ability to run just about everywhere and climb on just about everything. This gives you a good vantage point on where you need to go next. Also, this gives another dimension to fights with the guards, and knocking them off the rooftops is fun in and of itself. Jumping off of buildings, climbing towers, and grabbing onto ledges is simple and rarely misfires.
There are three main cities in the game, and you travel between them on horseback. There are a few different smaller towns that make the land feel real and alive. You never feel confined in the game, and are pretty much free to ride around to your heart's content. While there are no story progressing elements in the countryside, there are other side quests to perform.
Assassin's Creed is a game that hits the ground running. You start off feeling powerful and able to beat up on a few guards at a time. As the game progresses, you become even more powerful via new skills (throwing weapons, better counters, etc.). You can dominate many enemies at a time late in the game with ease; all you need to have is a steady hand. Counter-attacking is as simple as pressing a button when someone swings at you. As you log more and more hours, this becomes second nature. Even though enemies become tougher later on, counter-attacking remains simple and dispatching the baddies is no sweat.
To wrap up, Assassin's Creed is a fun and enjoyable experience that is worth playing. The story is engaging, but never forces you to progress through it if you are having too much fun killing guards. This is a game that has no serious weakness, and will occupy your time for many good hours.