Disclaimer: I've only played up to Assassin's Creed: Rogue. But that's still eight games.
Assassin's Creed is a popular AAA franchise that has the structure of a sort of "open-world" game with a main questline that is the only thing worth doing in the game (I should probably make an article about that). The story's revolves around a machine called the Animus that allows subjects to relive the memories of their ancestors. The player uses this to explore the distant past and learn about a timless conflict between two secret groups: the Templars, who seek world peace through control, and the Assassins, who seek world peace without sacrificing individual liberty.
I actually think the story is reasonably good for the first few installments, so my criticism is going to center on the game mechanics. There are a few different types of challenges the game offers: combat, chases, and stealth sequences.
The combat is shallow, degenerate, and easy. There are a lot of facets to the problems:
No matter how many enemies you get surrounded by, they don't really attack you. Every few seconds one of the six who can reach you will swing, but they never attack at the same time. This makes the combat very shallow, since dealing with six encircling enemies isn't much different from dealing with one.
The timing window to counter an enemy attack is much too wide. (And of course the games don't have difficulty settings - why would a AAA game designer do something so considerate of player enjoyment?). Add that to the fact that in some of the games it seems like mashing the button will make your character automatically counter everything - I noticed this happening at least in Revelations.
There's almost no reason for you to ever use the attack button. Most enemies take several attacks to kill, but if you wait for them to attack you and then counterattack, you kill them instantly.
For a few of the games, they did partially fix the problem of counterattacks being the omnipotent answer to everything. Some of the Ezio games (I think Brotherhood and Revelations) have this only work on some enemies while other enemies require similar but harder gimmicks. But Revelations had a problem even worse to make up for it: enemies with literally no counter play. It was the first game with enemies that had guns, and they didn't feel the need to give the player any way to combat this. You can't dodge it. You can't block or counter it. You can't use other enemies as human shields (they added this ability for the later games). And you can't kill them before they shoot you.
There's also the balance of weapons. After the first Assassin's Creed game, the hidden blade can be used as a normal weapon, and I found it to be by far the best one in the game for any situation. It's only drawback is attack damage, but as I've said that doesn't matter very much since instakill counterattacks are all you need, and the hidden blade is faster than everything else.
This isn't true of all the games, but in some of them you're just almost invincible. Assassin's Creed 1 and 3 in particular give you about twenty hits even without counting the ridiculously fast regeneration you have. In Assassin's Creed 2 and Brotherhood, instead of that, they give you "medicine", which you can use instantly for a full health refill and can carry up to fifteen vials.
The biggest problem with the chase scenes is the movement mechanics. There's a lot of ambiguity in your limited controller input, and so often your character has to guess what you want - which should be easy based on context - but he's very often wrong in ways you can't predict or account for. One example I like to ridicule is that when you're running toward a chest-high wall needing to vault over it, sometimes your Assassin just stops in front of the wall and won't move. Too late, time to go back to the last checkpoint...
Let's also mention how insanely scripted the path you take is in some of these scenes. In the last one in Assassin's Creed 3, you have to run through a burning and collapsing ship, and there's only one path the game will let you take, but it doesn't force you to take that path or give you any indication of what it is. If you step in the wrong spot, your Assassin will either get stuck on thin air or be stunned by a scripted explosion that you couldn't have seen coming. The result is trial and error gameplay where each time you fail you lose an entire minute or two of progress.
The guards' AI is inscrutable. It often seems inconsistent whether a spot counts as in their view, or whether they'll investigate when you're in view and duck into a bush (yes, sometimes that works), or how long it takes their suspicion meter to start draining. All too often, it comes down to hiding in a bush for twenty seconds watching the guard teeter on indecision about whether to check the bush, and it seems like there's nothing you can do about it.
They guards don't have ears, and don't even raise an alarm when they see a dead body.
And yet, these sequences are incredibly hard sometimes. That's because they put you in situations that would be beyond impossible to sneak through in real life. They also usually fail you instantly if you're caught. That part is especially frustrating given how easy combat is in this game (because you know you could easily fight off all the guards if the game would let you try). For several games of the series (most of the Ezio ones), the only way they could find to create difficulty was instant loss on detection. And most generally, the problem is that the game's movement mechanics just don't seem designed for stealth. In the first game stealth played a much smaller role and was never (to my memory) an instant loss condition. That was back when Ubisoft had the slightest idea what they were doing and what it entailed for the player experience.
I guess there are also some pretty big story criticisms I could make, mostly Assassin's Creed 3 and on.
In particular the rescue mission in AC3. The Templars capture Desmond's dad and offer to trade him for the Apple of Eden - an artifact of immense power. The obvious question is why the Templars don't just kill Desmond and take it when he walks into their base alone carrying it. Why would a badguy do the reasonable thing? We writers can't be expected to come up with a legitimate way for the hero to win from a disadvantaged situation. So Desmond walks into the room they're holding his dad in, with some two dozen Templar guards, and what does he do? He uses the Apple of Eden to easily knock them all out and save his dad for free. The Templars knew how this thing works! If that was a possibility they would have been prepared for nothing if not that!
In Assassin's Creed: Rogue, the one where they explore you playing as an assassin turned Templar, Shay's betrayal of the assassin order is literally based entirely on miscommunication. He is sent by his assassin commander Achilles to a city to retrieve an artifact, and when he does, the city is destroyed
by the plot by a questionable mix of earthquake and random explosions and fire. So "of course" Shay "logically" assumes when he gets back that Achilles knew this would happen and didn't care; and Achilles makes no effort to explain himself, but is enraged that Shay would insult him like this and tells the other assassins to "get him out of here" (while we as the audience know that Achilles is a goodguy and must have not known about this). No wonder Shay changed sides! It wasn't actually based on philosophy at all!
After AC3, it seems like they've just given up on the real world story. AC3 ended on a massive cliffhanger that left the entire planet with an ambiguous fate. The next two games, Black Flag and Rogue, do not the slightest thing to explain what happened. You play both as a throwaway character working for Abstergo Entertainment who has no lines no name and no face and the endings reveal absolutely nothing. How long has it been? Does the general public know anything about what happened in the end of AC3, or did the Templars manage to cover it all up? What the hell is this cult of Juno - MAY SHE GUIDE US INTO THE GREY - that popped up in Black Flag? How long have they been around? Were they part of things before? Are they going to be again? I saw the first couple hours of Assassin's Creed: Unity, and it looked very much like it's going to be another non-story and recycle the same horrible gameplay.
So don't play Assassin's Creed. If you played a few games before Unity and you're only continuing because you think it'll get better, it's not going to.