The controls are intimidating at first. But if you are not a novice player, you will understand pretty quickly how awesome they are and how much freedom they give the character. Basically you have a 'normal' mode of play and an 'extreme' mode of play. When you press the right trigger you enter the 'extreme' mode of play and everything you do, like walking, pushing are the more aggressive variant. So a normal walk becomes a run and a slow 'thinking trot' becomes sprinting plus jumping and a slight push to pass becomes a full grab to toss people out of the way or to push through crowds at high speed and tackle opponents. (riding on horse works similarly, easy trot and full gallop, etc. amazing animations on the horse, btw)
That's basically the entire premise. Use the 'normal' mode if you want to go undetected, strolling around the amazingly detailed, crowded HUGE SCALE cities and use extreme mode when you are on the run, scaling buildings, killing people from mid-air and hanging from rooftops, etc. It's crazy.
Guards will generally not be alerted to your presence, even if you run for a little, depending on their state of alarm or their patrol state, but they will get more aware of you if you bump into people and do crazy stuff. You can climb ladders no problem, but actually being on roofs may be a little suspicious to guards on the roofs. (This is also genius, there is actually a path to follow for the guards to most rooftops, since they are not free-run maniacs like you. Some are speedy and athletic though and can follow you pretty well when free-running later on). Generally you should not be near area’s where there is people you just killed, deranged people, thugs and guards with hands on swords. Otherwhilse you can walk pretty free until you do crazy stuff. Some chases can get totally amazing and long since when you are sprinting high speed through the streets to get away you are likely to attract more guards that set chase. I’ve literally seen tens of guards flood the roof where I hid in a curtained roof lounging area, who were apparently all alerted after a particularly long chase. Crazy sight!
Fighting the guards and characters is pretty well done too. You basically lock on to a target, but you are pretty free to lounge out to other characters involved in the fight. You kill with counter-moves and combo’s (which are both tricky at first). Also you can get grabbed and tossed, counter-toss, grab other weapons mid-fight (real-time weapons change) to finish opponents on the ground, etc. I love countering with the hidden blade, it has the most gruesome moves you can image, like impaling enemies heads with the blade, stabbing multiple times, etc. but you can’t actually block with it. Guards also do feints and some cower in fear, after you killed their mates. Great fighting engine! Also you can kill anyone on the street, but if it’s an innocent you will get punished for disrespecting the assassin’s creed. You can kill grandiose or stealth too. With stealth, you stab someone in the back and he will stay standing while you move away then fall, with the grandiose kill, you jump right on top of him and finish him for all to see. The later one works over greater distance then the silent kill, which has you standing virtually against the victim.
So the game is made just as well vertically as horizontally, on both 'planes' you have ample hiding spots to get rid of guards that may give chase, for example by sitting on a bench between some inconspicuous people while the guards run by, or in lavish roof-lounges with curtains, or in a group of praying monks, stacks of hay, etc. But you first have to lose line of sight, by either sprinting your ass off and using the citizens you helped for cover, they may hold chasing guards so you can escape, or taking to the roofs and just climbing like crazy until they can't follow you anymore, then jumping (with incredible style) into a cart with hay. The later jump points are always very subtly pointed out by you by for example flocks or birds sitting on a ledge (means you can jump there to a safe spot) or a particular texture, etc.
Climbing is amazing, you can grab every potruding part of a building, it just looks so good. The animations for the main character are truly a work of art.
Also, many don't know the game knows a very nice character progress system. It's not leveling, but it's close. You gain more 'life' points and weapons throughout the game by completing the missions. But, most important, you re-gain your lost abilities as you start the game as a demoted master assassin with only the basic skills.
The research for the kills is nicely done too, very in-detail if you want, you can plan the entire thing on the map, or you can just do the minimal work and see how it goes. Basically you do some pick pocketing, eavesdropping and interrogation to get information on positions of guards, the target, his habits, where you can find him, that will make the kill easier, since you can prepare by taking out guards beforehand, clearing a path and plotting escape etc. The kill itself is sometimes easier, sometimes tremendously hard to get done. Pretty challenging and nice to try a couple of times to see if you can find different ways.
Obviously don't want to give away too much, but the gaming world is basically five part. Three tremendously detailed and huge cities with their own style and lighting, (obviously they share some things) and the smaller (but amazing looking) home enclave of the assassins and also the Kingdom, which is a HUGE are with small villages, mountain passes and awesome design work and spots to explore.
Asides from the kill missions and the research you need to gather, there is tons of spots where you can help citizens and get some aid enlisted which may make things easier and there are like 400 flags to find around the world or something, all hidden at high and low spots, also some other cool 'search' missions where you will have to defeat a certain number or followers of a certain knighthood, hidden around the realms which are quite hard at the beginning since they have a full set of combat moves, and you almost none.
Favorites are also the missions you do for some other assassin's in the cities, killing people quietly or doing rooftop races and getting information in return. Also the pick pocketing rules! You can steal from thugs in the game, get throwing knives back you used, which is great fun. I feel there could have been much, much more of these sorts of missions, though, even if they were just unrelated to the story. Because they are so much fun.
The graphics are truly awe inspiring. Best animations and everythings ever. Never have my eyeballs witnessed such grandeur, scale and epic detail in a title. I really don't want to use more words to describe the utter genius and obviously monumental work, that went into designing this world. I’ll just use love.
Tiny footnote on the story: It's amazing and your brain will explode!