There are a few factors that make AC: Unity difficult to compare to my experience with the previous AC games.
First of all, other than stopping to do all the cafe missions as soon as they were available (to maximize cash income as I kept playing), I just went straight through all the story missions, ignoring all side missions and other activities unless it was something like a crowd even happening as I was running by or a treasure chest I was tripping over on my way to the next mission.
Typically I go back and forth, trying to play the story missions until the world opens up, then doing side missions/activities and getting collectibles for a while until I get too bored or progress is gated by advancing the story again. In both AC3 and Black Flag I was very close to 100% sync when I finished the final story mission, so this was a very different experience but it was based on my choice, not necessarily a difference in the game.
The story
So all that said, the story felt the least important in this game, in every way. There wasn’t much that was restricted by the story. I think you could pretty much go anywhere and do anything without advancing the story far at all. Most meaningful abilities were tied to equipment which you could save up and buy at any point, the specific “skills” you needed the main or co-op missions to unlock felt unnecessary, and when you did unlock something it was up to you what order to pursue your upgrades.
And the story was also pretty light-weight and unimportant narratively. Arno joins the Assassins to right a wrong, has his loyalties tested and questioned because he loves a Templar, he ends up choosing her over the Assassins and they pursue their vengeance together. The enemy is another Sage, who’s made himself a problem for the Assassins and the Templars, and he’s potentially a threat to the world via the normal aspirations of these characters to destabilize or disrupt society and governments from the shadows but he’s not about to grab a magic macguffin and end the world right there in 18th century Paris. It’s low stakes compared to the other games. And the modern world narrative is simply that they need to see Arno’s life played out because they want to know where the Sage’s body ended up, but you never experience the modern world in anything more than some transmissions into your game.
I think I prefer this.
The “Co-op”
I think you could have a party of friends or strangers and just run around doin’ assassin stuff with your assassin friends, but I’ve only worked specifically on the designated co-op missions and co-op heists. I really like that you can do both of these entirely solo. They’re long missions compared to the normal story and side missions—I guess they have to be since they’re built for up to four people to work on simultaneously—but that works well when you want a single player sort of sandbox experience for putting all your assassin skills to work. It has objectives, but fewer restrictions than regular missions. Those complaints I had earlier about never being quite sure what the rules are of the story missions—when should I be super sneaky and cautious, when should I just rush in violently—don’t really apply because in my experience both options are equally valid here, and there’s ample opportunity for both. I dig it.
I’ve got more I could ramble on about, and probably will eventually, but this is already a lot and I know no one’s exactly dying to hear more impressions of AC:Unity in 2018.