I'm not holding it against the movie, I'm only saying why I didn't like it as much. I still enjoyed it.
Re: fun to know beforehand: I tend to disagree. I can enjoy movies where I know the plot, but there's a difference between knowing "Rebels are on the ice world Hoth and have to fight against Imperial walkers" and "In the fight, Luke's ship is going to crash, at which point he'll run on foot to a walker, pull himself up, and use his lightsaber to take down a walker, after which Han takes Leia out on the Falcon and Luke goes to Dagobah where his ship will land in a swamp, and..."
So, you dislike watching movies multiple times.
There's a difference between watching a spoiled movie, and watching a movie you've seen before.
I have to agree. There are plenty of movies I enjoy watching multiple times, but watching a movie for the first time is unique. Maybe you'll catch something new on the second or twentieth viewing, but those viewings are generally about the same. You can't re-experience your first time.
A great example of this would be Memento. I have seen that movie at least a dozen times, and they're all enjoyable. None of the subsequent viewings blew my mind like the initial viewing, though.
I can't really speak too much about the plot twists in the original trilogy. I was 8 when I saw Empire. While I recognized the father revelation, it didn't register as monumental to my kid brain. The sister revelation was grokked better by my 11-year-old brain, though, but not enough to realize how silly that was getting. I'm sure that Empire could have been really cool for the adults in the theatre. It would have been like a soap opera...but with lightsabers.