Desmond Miles has problems. There's a deep, dark secret, hidden in his genes... and some people will do anything to get it out. Assassin's Creed is the tale of Desmond, or, more specifically, the tale of the mysterious ancestral assassin hidden in his DNA You'll spend most of the game in the shoes of Altair, the aforementioned assassin, his great-great-great-great (well, you get the idea)-grandfather, one of the infamous Hashshashin who tried to drive the Crusaders out of holy lands. As you experience Altair's history, you'll periodically have a chance to find out more of what's going on in the present, slowly unlocking Desmond's own story along the way.

While experiencing that history, the first thing you're likely to notice is the natural ease of the game's controls. Take the sheer joy of motion that Prince of Persia brought to the third person action genre and place it in life-size replicas of ancient cities instead of tiny obstacle courses. Altair climbs, runs, and jumps across rooftops with a grace and ease that make his motions a joy to control. There's never a feeling of fighting the controls to do what you want – the game creates an incredibly simple foundation, using one face button to trigger leg actions, one each for the left and right hand, one for a free look with the head, and a trigger to switch between low profile (stealth) and high profile (action) modes. It may sound a bit complicated on paper, but in practice, it engraves itself in your memory so quickly that guiding his parkour-style rooftop running is as effortless as it is thrilling.

Combat is similarly well designed. As you make progress in the game, you unlock new weapons and moves with satisfying regularity. You gaining new ways to defeat your enemies and new tactical options nearly as quickly as you become accustomed to what you already have. The most important combat upgrade is the countering system, allowing you to sidestep enemy attacks and execute a devastating counter attack, frequently killing the enemy in one flashy move. As you perform those flashy executions, you'll notice another strength of Assassin's Creed, shared between the combat and free-running systems – flawless animations.

Altair moves like a big cat, grace and restrained lethality evident in his movements. Uniquely, every one of those movements is perfectly in sync with the world around him. Altair doesn't have a generic climbing animation or a preset way to leap and grab things – he moves like a real human, reaching out to grab whatever handhold happens to be convenient, wedging his toes into cracks, arching and contorting his body in response to the object he's climbing. When he hurtles through space, fingers stretching out for a ledge or beam that's just barely within reach, his body reacts like a real physical object, an actual body with mass and momentum. There's an incredible sense of physicality to his movements, a feeling that you're controlling a real person with a real sense of balance, not just a set of animations. At all times, Altair seems absolutely connected to his environment. He is pure joy to watch and control. Unfortunately, that makes the time you spend as Desmond all the more disappointing.

Desmond, unfortunately, controls more like an arthritic invalid than the young bartender he's supposed to be. Where Altair handles with fluid, graceful ease, Desmond shuffles about slowly, and controlling him feels more like driving a tank than a person. Matters aren't helped by the fact that there's little to do when you're playing Desmond – there are a few chances to snatch some extra back-story, conversations to listen to, and a couple secrets to be found – one, significantly, after the end of the game – but for the most part, you walk back and forth in an area the size of a small apartment, doing little more than waiting to get back to the assassinating.

It's clear that the developers spent incredible resources of time on crafting three huge cities, each building modeled and placed by hand, adjusted and tweaked, not just to create a massive, convincing simulacrum of the ancient cities of Acre, Jerusalem, and Damascus; but also to create avenues and corridors for rooftop travel and escapes. The amount of time and detail spent there is incredible – so why, as you roam these sprawling metropolises, do you hear the same five or six sound bytes, over and over again, from the pedestrians below? Why does every one of the civilians you rescue thank you in one of two set ways? Why are you constantly accosted by beggars who repeat, word for word, the same script, regardless of the city or location?

For that matter, why are you asked, on more than one occasion, to run across the city and retrieve flags for an informant, in order to earn pieces of information on your next target? The flag runs may be slightly amusing the first time you encounter them, but they feel like they belong in an entirely different game. What in the world is a deadly, subtle assassin doing, skipping over rooftops to pick up twenty or thirty flags, each one emblazoned with the crest of the assassin's guild? It's a laughably silly activity that feels as if it was added at the last minute, as if a focus test decided there wasn't enough to do, and this was the begrudging response.