From a general point of view, it's better than Origins.
There are things which I have love and hate, like the Zack Snyder movies.

Graphics
No complaints. Fantastic visual effects, with clear improvements compared to Origins, especially in character modeling. I don't have much more to say, see for yourself.
The world map is clearly bigger. In addition to having the base of Origins, they also added the Black Flag to the mix, as ship travel is back. But it's still not being used very well...

Story
Imagine a kinda Zero to Hero story, like Luke Skywalker in Star Wars or Harry Potter. You are Alexios or Kassandra, a Spartan warrior who must find his/her place in ancient Greece during the Peloponnesian War, while unraveling the mystery of his/her own family.
Compared to Origins, I found a more captivating and mysterious story.
Like any recent AC, there are tons of side missions to explore, which I think is a bit of an exaggeration. But this can be relative, some people like it. This time, several missions are worth it.

Gameplay
It's where there are more differences, some good, others not so.
In Origins we had Senu, this time we have Ikaros. Except the name, it's the same thing.
The combat system is slightly better, it continues to be able to change depending on the abilities and weapon, although these are easier to activate during a combat. It's not really extraordinary, but little by little it's there.
The level system remains the most annoying thing I have ever seen. It is incredibly unnecessary. If Ubisoft wants to insist on that, just do it in a way that doesn’t affect the fighting against certain opponents so much. Right now it’s disproportionate.
Now the type of game is where the biggest difference is. From the first AC to Origins, we had an action / adventure and infiltration game.
But Odyssey now it is also an RPG.
I must say, it's a system that they could have implemented a long time ago. The missions differ depending on the choices you make and everything ... Basically, they were based even more on The Witcher 3.
But the shield I used to have on Origins disappeared. Why?

Soundtrack
It's much better. More impactful and appropriate, and blends very well with the environment while playing.
But the soundtracks of Jesper Kyd and Lorne Balfe from the first games still remain undefeated.

Conclusion
It's a better game. Adding the RPG system made the difference.
Grinding is still excessive and frustrating. Just don't stick only to the main story.
It's basically the culmination of the last 3 or 4 previous games, and I definitely recommend it.
My new favorite from the most recent series.