1. serving as an eyeopener; enlightening: ex) an eye-opening investigation of government corruption. (Random House Dictionar via Dictionary.com)
2(1). causing a strong emotional reaction because of unexpectedness: ex) hunting for a first apartment in a big city is an eye-opening experience for young people.
2(2). causing wonder or astonishment: ex) that acclaimed animal-cum-magic act had a number of eye-opening moments. (Merriam-Webster Thesaurus)
3. eye-opener. something that surprises you and teaches you new facts about life, people, etc.: ex) Living in another country can be a real eye-opener. (Cambridge Advanced Learner's Dictionary & Thesaurus)
4. eye-opening. (of an event or situation) unexpectedly enlightening: ex) this documentary should be an eye-opening experience to all. (Oxford Dictionary-US)