Anyone with two brain cells to rub together should have seen the Revan reveal from a mile away. It was so obvious that you had to literally not pay attention at all to not see it coming.
Well, by the time I got around to playing the original KOTOR (I played TSL when I was younger...), I had already named my character "Revan" at the start. So it wasn't much of a surprise, but it was a little comical as my character protested to his allies, "You don't understand! I'm not Revan anymore, I'm Revan now!"
Honestly, I don't even remember my first time watching Empire, so I can't say whether or not it was a surprise for me. The only Star Wars movies I remember my first viewing of are Revenge of the Sith and The Force Awakens.