I bought a DVD copy of this film last year. It was on the bargain shelf in a local supermarket. I watched the film when I was a kid once and I liked it, but it didn't leave a mark like other animated films of my youth. I wanted to watch it again. I was fascinated by the themes of hope and wonder, it is a really well crafted film. Each character has a great characterization, the voice acting is great, the animation is top notch. I think is just that great.
And one theme that resonated with me is the power of storytelling. It has almost a "All Star Superman" vibe, in which this character who is set up to inspire the best in everyone, actually inspires this Iron Giant character into something better. And I have yet to see that in a Superman film. At least in cinema.