I think it is a valid question...("other than what we know") because the discoveries of stratification, water, oxygen have all been previously revealed prior to this mission. What may lay ahead is the real question. What will we learn that is outside of our knowledge?
That's true only up to a point. Although it was known that liquid water had existed on the surface of Mars in the past what was not know was whether that water was pure or so laden with chemicals that life would be hard/difficult (think Dead Sea on Earth).
Curiosity has shown that fresh water existed on Mars, water that would probably have been pure enough to drink. That in itself is an important discovery made already by this mission.