It's a generally accepted notion that Assassins assassinate people. That's their job - it's what they do. But what you might not know is that in 1191 AD assassination work involves lots and lots of climbing. Walls, houses, towers, cathedrals, you name it, an assassin must scale it - bare handed, mind you.

At least that's how things work in the world of Assassin's Creed, the wildly original third-person action/adventure from Ubisoft. Set in the Holy Land during the Third Crusade in the cities of Jerusalem, Acre and Damascus, Assassin's Creed melds action with stealth gameplay in a gorgeous, convincing sandbox environment. Filled with excruciating detail, this game raises the bar of the genre to a new high - an altitude last attained by the classic Thief series.

The first thing you'll notice about Assassin's Creed is that it's stunningly beautiful. This game is the first of the next-gen HD titles to truly deserve the moniker "next-gen" - in my book, anyway. I don't care how many times you come back to this game, its visuals never fail to impress. The environment is a world of endless daylight, where the sun's harsh rays beat down mercilessly upon every street, structure and person in sight. You'd think that under such bright conditions, design flaws - every badly mapped texture, every poorly-modeled object - would be exposed. Not so in Assassin's Creed. The game's polished, detailed environment thrives in the garish light of day (broken occasionally by moving shadows of clouds passing), with resplendently realistic surfaces. The citizens who roam the cities and countryside anre meticulously modeled, wearing robes and tunics that authentically flow in the breeze as they walk.

The most detailed of all is Altair (All-tah-ear), the titular assassin under our control. His garb is scarily lifelike, replete with a realistic arsenal of weapons strapped to his belt and back and a retractable blade attached to his arm. And talk about flowing robes - Altair's garment is nothing short of dazzling in the way that it reacts with his movement and the environment. It's something you just have to see to believe.

As the game begins Altair is an assassin at the top of his game. But because of a misstep in which he breaks the tenets of the Creed, he is stripped of all weapons and demoted to the rank of novice. His master, Al Mualim tasks him with assassinating nine men - each with important ties to the Crusade - as a way to make amends for his betrayal. Each successful slaying earns you a higher rank and access to your confiscated weapons, giving you just enough power to complete the next assassination.

Essentially, gameplay boils down to this: Travel to a city; accomplish tasks that provide information to help you carry out the assassination; assassinate; escape. Within this structure, though, is enough variation to keep you playing for a long, long time.

When you arrive at a city, your first task is check in with the local Assassin's Bureau. But the city is completely foreign to you, so you must acquaint yourself in order to find the Bureau. To do this you scale the tallest structure you can find and scan the area. These structures - called "viewpoints" - are scattered in cities and across the Kingdom. At the top of a viewpoint you "synchronize" with the environment, after which the Bureau appears on the map. The act of synchronizing launches the camera into a magnificent sweeping arc around the viewpoint, showing the surrounding environment with Altair perched atop the tower as the centerpiece - a scene that never, ever gets old. You can see an entire city and far into the horizon - the draw distance in this game is remarkable.

After you've checked in at the local Bureau it's time to start your investigations, which come in several forms: eavesdropping, interrogation, informers and pickpocketing. You must complete a minimum of these before the Bureau will allow you to carry out an assassination - the rest are optional but it behooves you to complete them all in order to guarantee a successful slaying. You find these by synchronizing at more viewpoints.

Investigations comprise the meat of the game - you'll spend most of your time tackling them, with brief assassination segments interspersed. Luckily the tasks are varied, enjoyable and challenging. An informer will typically require you to perform a deed for him - such as assassinating a few men without getting caught - before he'll divulge his secrets. A particular individual may possess written evidence of import which you'll need to pickpocket from him. You may need to pummel a guy into submission before he'll let you interrogate him, and sometimes he'll flee, quite a hassle.

Aside from the interrogations there are other tasks to accomplish that, in some way, will benefit you. For instance, in every city you'll find groups of soldiers harassing innocent citizens. You can choose either to save the poor innocent who's being tormented or let the harassment go on forever (which it does if you don't stop it). Kill all of the offending soldiers and the citizen expresses his or her gratitude in a couple of ways. She may spread word of your gallantry, which convinces a group of local men to become "vigilantes," who block the way of pursuing soldiers while you escape. This comes in very handy after you complete an assassination and practically the whole town is out to kill you.

At other times saving a citizen will create a group of "scholars" that wanders around a certain area, waiting to help you. If you can slip into their roaming cluster without being seen you will become invisible to soldiers on your tail. Scholars are also useful for entering cities since, as a rule, soldiers will not grant you passage through a city's entrance. Soldiers will, however, happily move out of the way for a group of respected scholars.

Subsidiary (i.e., non-essential) objectives add to the life of the game, especially for players who love to squeeze every last secret and achievement out of it. One such task involves murdering a number of "Templars" - uber soldiers who are particularly bad-ass compared to the rank and file. These guys put up a good fight, so it's best to stealth assassinate them rather than face them head on. Also, there are hundreds of little flags planted about the kingdom and in cities, some in plain site but most hidden in nooks and crannies. Collecting all of these requires dedication and a willingness to sacrifice many, many hours for somewhat mild satisfaction.

The pinnacle of each mission is, of course, assassinating the next man on your hit list. Each of these figures is a heinous lout who deserves what's coming to him but they're typically guarded very well, making a stealthy assassination difficult. Each attempt starts off with an in-game cut scene that sets up the situation, after which you dive in and go for broke. Not surprisingly, assassinations are the most challenging aspect of the game, and completing one provides a tangible sense of accomplishment.

Simply said, there's quite a lot to do in Assassin's Creed. When you're not focusing on a task there's plenty of landscape to explore in the Kingdom outside the cities. Hop on a horse - any horse - and gallop around the world to check out all of the gorgeous detail. Synchronizing on viewpoints outside of cities provides a spectacular view of the almost painterly mountains, cliffs and shimmering bodies of water that make up the world.

There's something exhilarating about leaping from rooftop to rooftop with abandon, slaying soldiers along the way. Altair possesses seemingly endless energy, every action graceful and smooth. The controls for Altair are particularly well implemented, making his constant climbing a pleasure to navigate. Once you get him onto a wall, scaling it is just a matter of guiding him towards things he can grab onto, like protruding bricks or window ledges. He responds dutifully to your direction and can climb even the most daunting of structures. One cathedral steeple in particular takes Altair to an astonishing altitude. Once at a summit, Altair need not climb back down, for he has the ability to perform a "leap of faith," which lets him dive from even impossible heights and still land safely in a bale of hay. Great stuff.

I'm equally impressed with the game's save-game system. Rather than let you save at any point, the game saves your progress automatically right after you accomplish an objective and at various checkpoints. You're accomplishing things so frequently that your saved game is always up to date and rarely lands you in a sticky situation. Even if you die after you've completed an assassination the game doesn't take away your success - it simply loads directly after the slaying (typically with you surrounded by pissed-off soldiers). The one downside to this save-game system is that there is only one save available - you can't go back to an earlier saved game to try something differently, so make sure you do things right the first time.

Disappointments are few in Assassin's Creed, but there are several elements that, though they don't ruin the experience, certainly provide some annoyance. Although the camera movement is pretty good in general, one thing I can't stand is its limited field of vision. It's most noticeable when Altair is standing near a structure - I often find myself craning my neck trying to see things maddeningly just out of frame.

Another limitation that seems unnecessary is that Altair, who possesses incredible gymnastic prowess, is unable to swim and dies immediately if he hits water. I have a hard time suspending my disbelief on that one. It's a pointless omission. There's so much variation and detail crammed into the game that it's hard to imagine why some elements didn't share the same attention. For instance, the voice work in the game is extremely well done, but there are so few variations in dialogue that much of citizens' banter becomes repetitive. "You dare steal in my presence? That will cost you your life!" - shouted by one particular soldier who apparently works in every town - is one phrase that I'd be only too glad to never hear again. The patter of persistent beggar women is also infuriatingly repeated throughout. Luckily, guards look the other way at fistfights and punching a beggar makes her run away. (Drawing a weapon has the same effect, but I prefer to clobber them - it just makes me feel better.)

And unfortunately, the game's difficulty level falls victim to the "more is harder" approach - increased difficulty means an increased number of soldiers thrown at you, with local thugs only too happy to take a swing at you, until fighting is nearly all you can do.

Despite these peccadilloes the game always manages to redeem itself. After dying five dozen times at the hands of a mob of soldiers I may be ready to chuck the controller out the window, when suddenly I spy a citizen who stops walking to check the sole of his shoe, or pause briefly to sneeze or brush dirt off of her tunic. Leave Altair idle while mounted on a horse and he pets the animal's neck assuringly. And each city has its own distinct lighting, one a bluish tint, another greenish and another bright yellow, as well as clouds of dust that hang just above the city's dirt streets. As well, the well-crafted orchestral music has an "Arabian Nights" flair to it that switches to menacing percussion and atonal harmonies when you're in trouble with the law.

Assassin's Creed is the most satisfying gaming experience I've had in recent memory, replacing Bioshock, which still ranks pretty high. What pushed Assassin's Creed ahead fpr me is the verisimilitude of the game's historically accurate environment. Don't get me wrong, I love Bioshock's fantastic Art Deco aesthetic, but at the end of the day the world of that unique underwater metropolis just doesn't make much sense. Assassin's Creed dumps you right into the middle of a thriving, historical culture that feels incredibly authentic. Tramping through the streets of Jerusalem in 1191 AD with its exasperating beggar women, belligerent mental patients and local women carrying pots precariously on their heads is an experience second to none.