The primary flavor is oregano, pungent Greek oregano if possible. That's combined with salt and pepper, dried garlic, and perhaps mint. A Pinch of thyme may go in too.
I think it is the combination of spices used in greek meat seasoning that gives it good flavor. I taste garlic, cumin, oregano, cucumbers, onion , salt & pepper. I think some may also use wine or a yougart base.