Well... I am not used to seeing other gamers give so much thought to what I would call my 2nd favorite game series so that is something. At this point, I only thread the first page but I want to start jumping in bit by bit, so lemme explain why AC means so much to me.
The tl;dr version is AC2 is responsible for me getting back into gaming as an adult and caring it about it enough to become an Escapit+ member and such.
I'm 44 so I got into games as an 80's kid and 90's teen: arcades and the Nintendo-led home console revival, with Super Mario 3, Link to the Past and Street Fighter 2 representing the pinnace of my youngblood gaming life.
I pretty much abandoned solo/serious gaming in the late '90's when I went into college and spent my time with other things (school, work, and other shall we see non-productive pursuits). This means that I pretty much skipped the revolutions in FPS, PC, digital RPG and 3D gaming. While Half-Life, Halo, FF7, GoldenEye, and Baldur's Gate redefined gaming, I was nowhere to be found. To this day, I still can't even play FPS games. I mean sure I would mess around with friends and I had PlayStations that I barely turned on for like Guitar Hero or whatever but that's it. My entertainment interests were more about music (still my #1 thing) and film, boy did I become a film nerd.
in my early '30's I was spending a lot of time alone and I got a cheap PS3 somehow and jumped back into gaming and was floored by the cinematic games of the Uncharted, Assassins Creed, and God of War games. To me, it was like stepping into the future.
But it was AC2 that hooked me so hard that my passion for film energy started to transfer to games as a medium for the greatest art & entertainment other than music. I couldn't believe I'm playing in Italy.. like, the real historical Italy, with the pope and Medecis, and in a way that lets me climb and run everywhere. And the humor, the characters, the wacky conspiracy stories, I was floored. The bits with the puzzles that reveal how the Templars are behind every crazy thing in the world enraptured me.
I have played this game like 20 times and for me it's like how so many can which Goodfellas for the millionth time and love it- I would happily replay that shit right now.
I say all this because my love of AC2 and the franchise is with the complete agreement of all of OP's criticisms. Yeah, the pacing and narrative shortcuts of AC2 are glaring. I just.. don't care, I guess?
Of course I played AC1 and I gotta say, I think that game is also pretty awesome. Sure, as many say it is like a prototype, and there's a lot of stuff they meant to put in and didn't and it's obvious (The Kingdom!). But the setting, story and vibe are actually so amazing. Have you ever tried to play it without HUD? It totally works. It is the only AC game that was designed for that. You can use environment cues to really feel like a shadow-y assassin tracking your target. It's really great and I highly recommend it.