surprising
Unexpected and causing you to feel wonder or shock.
Surprising means unexpected or causing wonder because something happened differently than you thought it would. When your quiet classmate suddenly raises her hand and delivers a brilliant speech, that's surprising. When you open what looks like a boring book and discover an adventure story that keeps you reading past bedtime, that's surprising too.
Something surprising catches you off guard, in ways small or large. A surprise party is surprising because you had no idea your friends were planning it. A plot twist in a movie is surprising when it changes everything you thought you knew about the story. Scientists make surprising discoveries when their experiments reveal something nobody predicted.
Notice that surprising isn't always pleasant: a surprisingly difficult test can disappoint you, while a surprisingly easy one might delight you. Either way, the result differed from your expectations.
Sometimes people use surprising to suggest something should have been obvious but wasn't. If a student who never studies fails a test, you might say, “That's not surprising.” Here, the word points out that the outcome was actually quite predictable, just not to the person experiencing it.