The idea that someone thought they liked a movie while watching it in the Theatre, and then realized they didn't like it is kinda strange to me.
Certainly there have been movies or TV shows, that when I first gave them a try, they didn't appeal to me all that much, but, on a second viewing I liked them more (either because I was in the right mindset to enjoy it the second time, or it was years later, and I changed as a person, etc). And certainly, there are movies and TV shows that you just don't like as much the second (or more times) viewing.
But, to sit there only thinking you're enjoying it while watching it, and then thinking about it afterwards and deciding you didn't like it afterall, is just incomprehensible to me?
I, too, agree, they should have left John Harrison as John Harrison, and not had him turn out to be Khan, but, that didn't ruin the movie for me, and I still love it as much as I loved it in the Theater, and it's still in the top few of my favorite Trek Films