I've played a lot of open world games, but origins has to be the most enormous, immersive, and organic one. The missions in Origins is vastly improved from previous titles, even side quests. They don't feel repetitive at all. I rarely have the urge to play side quests in most games, because they feel like fillers, but the side quests in Origins feel organic. They have good cutscenes and dialogue that make you feel like it ties in with the main quest. The mini plot in the side quests are interesting too.
At first, the controls were really weird. Shoulder buttons were the main action buttons, but once I switched it to the alternate controls, it was much better. The combat is more difficult since there isn't any parry prompts, but it's still very playable. Stealth isn't as free as it was. Enemies are more aware, but you get an eagle that you can summon to scout the entire area. This was a very nice addition since it allowed the player to manually recon the place, instead of having the points of interest shown automatically.
The narrative is my favorite. The relationship between Bayek and Aya is heart felt. You care about their cause, and want to fight for it. It's also very interesting how the story tells how the Assassin Brotherhood formed. All the other characters are good too. Very interesting death scenes, where you get to know the true intentions and thoughts of the templars. There are plenty of cinematics and dialogues in this game, which add so much to the narrative. I also loved the monologues from Bayek, as it added to his personality.
If you like open world adventure games, you can't miss Origins. This is the best in that genre I've ever played.