The awkward, clunky combat REALLY takes away from the experience. The combat mechanics are a substantial downgrade even from the Ezio arc (not even talking about Origins/Odyssey/Valhalla) - nothing feels fluid, and every fight is a total slog. This might have been a deliberate choice to make the players focus more on stealth, but it very much detracts from the overall gameplay.
The climbing, too, feels like actual WORK. I don't mind at all that it's more restrictive than it has been in Odyssey/Valhalla, since those were rather too permissive (imo) and didn't require any forethought. What I DO mind is that the character doesn't react smoothly even in the spots where he is able to climb: it feels more akin to climbing in Ghost of Tsushima than to previous AC installments.
It's really unfortunate, since the rest of the game is pretty damn cool, especially for those of us who have been with the series since the beginning. The stealth mechanics are excellent, the pickpocketing is very well done, the parkour is for the most part perfectly workable, and by the game's midpoint you do get enough nifty toys to enable you to avoid combat almost entirely.
It's definitely more focused and narrower in scope than any of the games since the original, but I certainly feel like I got my money's worth. I loved the open setting of its three precursors, but I also don't feel cheated by a shorter but more tightly structured game.