AC made a great game, but there are too many things that you have to keep track of. 90 minutes just wont be enough time to unwrap each of them in a way that is even remotely satisfying.
There'll be two plots - one inside the animus, one outside. Two is too many for 90 mins.
The animus itself is a huge stretch, and you know they will just "plug it in and go" rather than actually take time to ease the audience into it (e.g. the way the matrix did; training programs, lengthy explanations, etc.).
Parkour for the sake of Parkour just sucks in movies. If this was more "Jackie Chan" and less "check out how many sweet backflips I can do before I kick you" I would have higher expectations.
You KNOW this movie is going to be hated my one or more religious groups. Not sure which group yet, but it'll come soon.
Establishing the Assassins was fairly well done in the first game imo. It will absolutely not be well done in this movie, guaranteed. 90 mins just isn't enough time.
It's just so unlikely to be good. I hope it is good, but it won't be.