I was blown away by Origins. Getting to visit the pyramids and the sphinx. Running around Alexandria, recreated at the height of its glory. It was stunning. After that? Oh look... more sand. I got bored pretty quickly, abandoning the game maybe a third of the way through?
Odyssey is a different beast. The cast of recognisable people and places is far greater. The Peloponnesian War provides a much more interesting backdrop than the story of Caesar and Cleopatra, and works as a distraction to the jarring AC sci-fi nonsense. The addition of naval combat and the development of the mercinary system help to vary the gameplay.
I've also grown to love those moments where an assassination goes completely wrong. You're perched above your target; the opportunity to strike has come. You hit the "assassinate" button, and realise (too late) that the attack won't kill the enemy. Suddenly you're fighting half a dozen soldiers, while the alarm is raised. More reinforcements appear, along with the two mercenaries who have been tracking you. One of the mercs is a couple of levels higher than you, has a pet bear, and throws fire grenades. Chaos ensues