No surprises if you study & prepare. Master the Study Guide given to you. Read the Quick Reference Card & Memory Items. Learn your limitations (speeds, weights, fuel capacity, altitudes).

Examiners can ask questions outside the study guide but as I understand they can only fail you if you don't know the material from the study guide. My examiner focused on first level knowledge (they're not expecting you to, proverbially speaking, build the plane) but focused on scenario based questions that forced critical thinking. Crazy as it sounds, I actually enjoyed the oral and learned a lot.