Also, I know I've talked about Odyssey's combat, but I'm gonna talk about the stealth now. Now, I didn't play enough of Origins to know if it was the same (and it was probably at least similar), but man, they have massively improved sneaking around in this game compared to previous entries.
One of the things I always hated about playing Assassin's Creed games is that the stealth was always dog shit. It was very difficult to go undetected in previous games. Borderline impossible much of the time. I remember how frustrated I'd get in AC3 and Black Flag when I'd try to be sneaky on missions in enemy territory where the slightest glimpse of you sends every guard in the world running straight to your location. And given that these games were titled Assassin's Creed, the lack of good stealth was really disappointing.
In Odyssey, though, I regularly make my way through entire enemy encampments, slowly picking them off one by one, hiding the bodies, and then looting the place clean once everyone is dead. It's very satisfying, even if it requires a lot of patience. But I love stealth games, so I'm fine with that.
They also give you quite a few different abilities that give you new options to help you stay hidden. You can upgrade your stealth so you make less noise when sneaking and when backstabbing guards. There's a mid-range attack where you chuck your broken spear at an enemy, effectively letting you backstab them from a distance (and you can chain it I think up to three times when fully upgraded). There's an overpower backstab that helps you deal with stronger enemies who might not fall to a regular backstab (it costs stamina, which you gain from killing enemies in normal ways).
And then there's the bow and arrow. I know ranged combat isn't really new to this series, but this is the first game I've played where it feels like a major part of it. Again, maybe Origins and some of the other newer games did this too, but this game has an entire skill tree dedicated to upgrading your bow and arrow abilities. Not only are their various abilities (like an overpowered arrow that, like the backstab, costs a bar of stamina), but you can also craft like five or six different types of arrows, including fire, poison, and explosive ones. This factors into stealth play, as obviously a bow and arrow makes for a much more silent kill than the pistols I remember from past games.
One further nice feature is that, when a guard sees you, you will get a brief couple of seconds (which you can upgrade to get a bit more time) to react as time slows. If you kill any alerted guards before time speeds back up, an alarm won't be raised.
It's hard to really quantify in words how much better the stealth is in Odyssey compared to the early games in the series. It feels more similar to Dishonored than previous games, as your various abilities make you a death-dealing force of nature when used right. There are still the typical Assassin's Creed issues where you never quite seem to jump exactly where you want to, and occasionally that will get you caught, but the game also added a quick save feature to help out in that regard. You can't save when you're in a hostile zone, but it's a pretty easy feat to off a guard or two, hide the bodies, then slip just outside the zone and save before sneaking back in and killing another couple of guys. Rinse, repeat.
Oh, and if you play Odyssey, I'd make the following recommendation: play as Kassandra. Her voice acting is just way better. Really glad I didn't pick Alexios, because I've seen videos of people playing with him and I hate his voice.