Height, scale, variation, complexity, spires, gullies, proc gen etc, preferably flying with others at silly speeds, in highly engineered, agile ships with plenty of rebuy credits.
To experience it, is to know the difference.
I can only say you should explore odyssey more. I've found all that and more. Canyons? Check. Spires? Check. Complexity? Check.
It took years to find the good canyons in Horizons, it stands to reason it will require similar effort to find them again in Odyssey.
Take this for example:

If there's one, it stands to reason there will be more. Just gotta hunt them down. Can't expect fdev to do everything for you.