How about films you HATED that you now LOVE!
For me it's '2001: A Space Odyssey'. A bizarre experience because I have never hated a movie more. There was just something about it that felt completely pointless and boring and it made me vow to never watch it again.
Luckily, my friend basically forced me to sit down and watch it again and it was like a completely different film. Since then, I've seen it about a hundred times and it just keeps getting better and better. It's a masterpiece and remains in my top 10.
Due to this, I made another vow (which I have actually stuck to) to never write a film off again after just one sitting.
So what's your choice!?