While the series has certainly suffered from sequel saturation (II and Black Flag are amazing while Brotherhood and Revelations have been kind of glorified expansion packs. I have yet to play Syndicate, which I hear is good,) there is a lot of compelling stuff to the Assassin's Creed games. I'm particularly a fan of the insane conspiracy theory stuff (best exemplified in II's Subject 16 puzzles.)
This film will be avoiding mixing up the canon by focusing on a non-Desmond character in the modern day and going to a setting the games haven't touched (the Spanish Inquisition.)
Cinematically, the trailer makes the movie look very much like the game, luxuriating in medieval architecture and filled with parkour-based action. I'm also one of the three or four AC players who actually liked having the modern stuff in the games to give context to the historical stuff (and was highly disappointed that the modern-day plot stuff in Black Flag was so incredibly superfluous and devoid of characterization,) so I'm glad to see that they're absolutely including Abstergo's modern-day Templars as part of the plot here.
I'm always going to save a little extra skepticism for video game movies based on track record, but the only note that rang really off to me in the trailer was the weird robot arm thing that seems to be the cinematic version of the animus.
Still, Michael Fassbender's a good actor, and there's other good cast members (though the presence of Jeremy Irons, fantastic actor that he is, in a game-based movie is no guarantee of quality, given that he was also in "Dungeons and Dragons" in 2000. Yeah, did you remember that that movie was a thing?)
While I don't think we can really expect this, I hope that they really make this feel like a prestige historical drama that gets interrupted by bursts of parkour-based violence and a sci-fi frame narrative.