Learn English – A word that means “interesting-ness”

How about wonderful?

I think the word you are looking for is greatness.

Shakespeare in Twelfth Night coined what is probably the most famous usage of this word

Be not afraid of greatness: some are born great, some achieve greatness and some have greatness thrust upon them.

Edit: You could also try exceptionality, but that is somewhat odd sounding, not very common, and in my opinion nowhere near as great as greatness.