The tragedy of the central plot mirrors the tragedy of the Revolution going on around it: in both cases, there is a chance for compromise, for unity (the title is ironic; notice that the Assassin logo is disunified, split and dislocated), but both the Laserre-Mirabeau modus vivendi and the prospect of a constitunional monarchy collapse as the hardliners and fanatics on both sides take bloody control (Mirabeau playing the conciliator role in both dramas). Bellec and Germain are St-Just and Robespierre writ small.
When Charles leaves Arno behind for his secret meeting in Versailles, he gives his son his pocket watch and tell him he would be back when the minute hand reaches the top. When Arno sees his father's body, he drops the watch which breaks on impact, preventing the minute hand to ever reaching the top.
The design of the guillotine is weirdly similar to the hidden blade. The hidden blade, held horizontally on the wrist, protrudes in a forward straight direction by a spring mechanism and is meant to insta-kill target and give them quick deaths. The guillotine was designed as a humane alternative to more cruel forms of capital punishment such as drawing and quartering, breaking on the wheel and likewise it has a mechanical lever mechanism that brings the blade down at great speed to instantly kills a person and so minimize pain. If you miniaturize the guillotine and hold it horizontally it might be similar to the hidden blade itself. The ACU logo, features the Guillotine Blade between the A, further honing the connection. The main difference is that the Hidden Blade is concealed, while guillotine is the national razor.
Arno sports a Blue Longcoat, a White vest and a Red Cravat, he's a walking French tricolor.
Why didn't Arno investigate further into his father's death? Arno probably believes even if de la Serre was involved in Charles's death, he's also dead. Arno's feelings for Elise also meant that he would not be able to investigate the murder without jeopardizing their relationship, which was already rocky enough when Elise believed Arno to be de la Serre's killer.
In a previous game, two characters discuss how Templars and Assassins have never been able to work together. In particular, one character mentions that the two sides "have never been able to achieve unity." One of the early trailers for this game reveals an Assassin freeing and fighting alongside a Templar, a nice bit of foreshadowing.
This game also shows why that's the case: everytime the more rational and level-headed Assassins and/or Templars (such as Comte de Mirabeau and François de la Serre, or Arno Dorian and Elise after them) try mending the gaps and enacting Enemy Mine for the benefit of humanity in general, the more radical and selfish elements on both groups (such as Pierre Bellec and Saint Germain) will betray and kill or expel them to keep the Forever War going over their own shortsighted grudges and/or self-interests. And given how William Miles explained it to Desmond, both sides will either omit from history and/or lie about any such attempted truces to dissuade the very idea. Both games end up reinforcing how, in the end, Templars and Assassins aren't that different in their flaws and fanaticisms.
Tied in with Assassin's Creed Rogue, the ending of the latter has Shay talk about how the Templars need to start their own revolution. Which means that in a backhanded way, the Assassins did start the French Revolution.
Why is Arno's Eagle Vision only available in short bursts? Since he isn't one of Desmond's ancestors, he doesn't have as much First Civilization DNA in his system as Altair, Ezio, and the Kenways do. Also, the Helix system is a gaming console, not a fully operational Animus, so players only have access to First Civ abilities in short bursts.
I think it's also a concentration thing, certain assassin's have limitations on how they can use Eagle vision, for example Edward cannot use it while running, while if memory serves Altair couldn't use it while moving at all. Perhaps, for those with the ability, the scope of their ability to use it depends on how well they can focus, perhaps a higher Isu DNA concentration reduces the amount of focus needed. In Arno's case, his Isu concentration is low enough that he has to really concentrate to use Eagle vision, enough that he begins to develop a headache, at which point he has to take a moment to relax his senses before using Eagle Vision again.
We've seen Assassin Councils before, namely in Brotherhood, where Machiavelli led but the rest of the Master Assassins were largely independent. The French Assassin Council seems much closer to a system of voting than those in the past, with Mirabeau still having some degree of veto power over them. The idea of a Council with a figure of greater authority over them with occasional veto powers bears resemblance to a constitutional monarchy, something Mirabeau advocated for greatly in Real Life.
The reason why Sequence 11, Memory 01 ("Bottom of the Barrel") was in such a strange blue tint was because Arno was severely depressed at that time after getting kicked out of the Brotherhood and falling out with Elise. The Animus not only allows us to relive genetic memories, but get an insight into the emotional state of the person while they were making those memories.
