Question

What should the conclusion leave readers with?

an opposing view point at the end

a new set of ideas at the end

an important thought at the end (This one?)

a confusing question at the end

Answer 1

the conclusion should leave readers with an important thought at the end.

Answer 2

I would agree with you - the conclusion should leave readers with an important thought at the end.
This thought should never be new, or opposing to the previous ideas you had been writing before. It also shouldn't be confusing, but quite conversely - it should explain everything and put everything in place.