These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Breather Level: Between the action-packed assassinations, Alta´r has to complete multiple relatively peaceful investigation missions.
Complete Monster: Majd Addin, the de facto dictator of Jerusalem, is a smug, strutting sadist of a man who takes full advantage of his position to carry out his wish of holding the lives and deaths of the populace in his face. Majd Addin regularly orders and carries out the executions of innocents for trumped up charges. Unlike his fellows, he has no illusions he is doing any good in the world. When Alta´r performs his assassination, one victim is even a prostitute who protests her only crime was not sleeping with Majd Addin. When he is confronted by Alta´r, Majd Addin gleefully explains he has done everything because he could, and holding the lives of others in his hands made him feel like a God.
Disappointing Last Level: Most of the game is built around stealth and free running in sprawling cityscapes. The last part is a linear, rigidly structured sequence in which you have to fight your way through dozens of opponents with no possibility of evasion or escape.
Best Level Ever: Thought for some this's the best level since you finally don't need to bother with stealth and just go all out Rambo style, with Robert de Sable and Al Mualim as the final bosses of great challenge for you to fight.
To a (much) lesser extent, Sibrand. He's the only Templar who has much presence in fandom.
The nameless Rafiq in Damascus, mostly for his cheery nature and amusing sarcasm. He's not as dour as the Acre Rafiq, or as bitter as Malik.
Game Breaker: Counter attacking with the hidden blade is a One-Hit Kill, even against the final boss (once you jump through his other hoops)... so long as you have the timing down enough to succeed consistently (key word here).
Not to mention, if you get the timing down well enough to consistently counter with the Hidden Blade in this game, you've just developed a skill that will make the entire rest of the series MUCH easier.
You can kill entire armies with the hidden blade. Throw two people to the ground and knife them, and others will start to recoil in horror or distract themselves. The ones who recoil can be assassinated before they recover, that assassination will make someone else react, and so on and so on...
Throwing knives can, especially in 2 and Brotherhood, be countered themselves, so a counter attack won't always kill, but throwing knives cannot be blocked. Even during a fight where the boss will block all your other attacks, throwing knives can make quick work of them.
The guards can feel like friggin' bats when you're trying to run and hide, and they pelt you with rocks as you climb away, or the alert goes off again just as you're about to dive into a rooftop garden. They also like continually spawning just after you've killed a bunch of them to save a citizen, immediately starting another fight.
There is also the beggars, who constantly harass you (and only you) for coins, and the lepers, who shove you (and only you), sometimes into a group of guards or an informer's assassination target.
The archers. Up close, they are just normal guards, but at a distance with their bows out they are unblockable. Throwing knives can easily kill them, but early on you only have five, and you have to either steal from thugs (whom you have to leave the rooftops to find) or return to Al-Mualim to restock them.
Hilarious in Hindsight: After one of the main Assassination targets used poison on some civilians, Alta´r makes a side comment to another Brotherhood member that poison is a coward's weapon. In Assassin's Creed II, one of the main character's weapons is poison. (A blade dipped in poison, to be exact)
Said blade was invented by Alta´r himself, as Da Vinci builds it from the designs in the Codex.
Many fans of the first game call Ezio weak because he uses dual hidden blades and his hidden gun. "Alta´r never needed those." Considering that it was Alta´r who invented them... well, what does that make him?
LGBT Fanbase: Malik and Alta´r. Strangely, due to the huge amount of Foe Yay between the two that lasts until about halfway through the game when Malik forgives Alta´r for costing him an arm and getting his brother killed. Though quite a bit of the resulting fan art set out to only tamely fill in the blanks of what Alta´r does when he rests at Malik's Hideout.◊
Memetic Badass: The In-Universe mechanics indicate that only a perfectly played game is canon, in turn implying that Alta´r was literally so badass that his enemies couldn't touch him. Keeping in mind that Alta´r is forced to fight dozens of opponents at once to the death at certain points. This has not escaped fans' notice.
The Memetic Badass page has more examples of Alta´r's awesome, but the best relates to desynchronization. The player (as Desmond) "de-syncs" with Alta´r if the player does something Alta´r doesn't remember doing. Being hit causes de-sync. Meaning Alta´r was never, ever hit.
Nausea Fuel: One of Alta´r's counter attacks with the short knife is an elbow to the stomach and a punch to the face, which leaves the victim standing there for a split second, dazed. You have the option of letting him fall and get back up again, or pressing X/Square to finish him off. If you finish him, Alta´r takes his knife in both hands, raises it above his head, and stabs the guy in the skull. Just... the sound effects (sounds like wet wood snapping in half) and the fact that Alta´r has trouble pulling the knife back out again... ugh.
Or you can stomp on his knee, folding his leg in half with a sickening crunch.
Anti-Climax Boss: Due to the game's mechanics, the fight with him can end quite abruptly if the player manages to knock him down early on in the fight and follow it up by stabbing him with the hidden blade as he lays on the ground. This can be done in a matter of seconds after the fight with him starts, effectively having Alta´r curbstomp the man who curbstompedhim at the beginning of the game.
Sybrand. Hop from boat to boat and prepare to miss jumps and drown or simply drown because the game decides to kick you off that surface you just jumped towards.
Uncanny Valley: The generic character models have simplified hands, the fingers stuck together in pairs. It leaves them looking like they have two broad fingers on each hand, and never stops being disturbing.