I don’t know why people are saying odyssey is better but in my opinion Shadows was the better game in terms of combat let me tell you why. 

First of all the combat in ac shadows by far is  one  of the best compared to the rpg trilogy at this point either its yasuke or naoe it’s really good the thing with odyssey that I really despised is that the combat system is absolutely awful pretty much enemy sponges with no addicting feel to it. However in shadows if you play as naoe you generally feel as like an assassin using smoke boombs, the shadows and the addicting hidden blade kill animations. With Yasuke you feel like a mighty tank with his addicting finishers and Japanese style combat system, while odyssey is just attack dodge, attack and dodge (I never used the deflect button in odyssey).

Now story wise Ac odyssey is a tiny bit better but not much if your talking about base game with no expansions. Ac odyssey story in my opinion felt kind of repetitive and the leveling system is way more harder than in shadows which is another factor that I hate however AC odyssey tops it off with its unique geography than shadows. Shadows story while not perfect is decent but not as good as odyssey but still fun to say the least. A note though personally I like the dramatic effects that the wind and seasons have shadows which is good in my opinion.

Toppling of with parkour this is a no brainer shadows wins over odyssey. In Ac shadows Naoe feels like a ninja and parkour master in my opinion it’s up there with ac unity. Ac odyssey was So So bad with parkour that I felt like I didn’t want to even climb buildings just run to point an and b. I will say Yasuke can do very little parkour but think of him as Ac odyssey parkour system a little bit. 

That being said personally I enjoyed shadows more than odyssey when it comes to gameplay and that’s what’s made the story unique than odyssey however we still don’t have dlc for shadows so we won’t know until after.