I loved Origins and have played a ton of it, like 120h +. I'm a few hours into COTP, so I could be misstaken. But from what I can tell there are no new mechanics at all. The new skills I was looking forward to are very disapointing. Basically they are just under-the-hood skills that tweak the damage output for your bows, or melee attacks. There's not a single new thing that you can actually do. No new animations for Bayek at all. On the surface the DLC is cool and I like visiting the classic locations. I'm just very disapointed we didn't get any new toys.
Season pass cost half of what the game did. I expected more to be honest. It would have been better if you only did COTP and added some new mechanics, than doing two DLCs just consisting of "more of the same".
To be frank I just feel bored playing through it.
Sadly, most devs anymore do not make changes to AI or animations after initial final release, including DLCs. It's not so bad if they include a lot of good animations at release, but AC has been known for some installments that were woefully short on animations. The worst for me was AC IV. Too bad too, because other than that it was a pretty good game. I really got sick of seeing Edward do nothing but twirl sword attacks though.