I can’t comment on Odyssey, bar what I’ve read from other places; pretty but over-long, essentially. I did recently buy Origins and have played all the others (I’m perpetually playing catch-up with the series), and to be honest, I don’t really know what they could do to innovate at this point.
The small changes here and there don’t really do anything for me, but the cyclical nature of the series can also be numbing and make me feel like I’m playing the same game over and over with a lick of paint applied to it. But I think any major overall would come with a cry of disappointment that it didn’t feel ass-creedy enough which they wouldn’t want to risk. In some ways, the key changes are a new historical theme and main character, and how loudly they’re riffing on the annoying sci-fi background noise in that particular version.
Basically I think they’ve painted themselves into a corner where their games are little different to a new instalment of Fifa. Not necessarily a bad thing; certainly less interesting. I assume they don’t mind, if it keeps making money.