First, the clone wars. There was just that one mention by Obi Wan in the first movie, and I didn't really pay much attention to it. After reading Zahn's trilogy, the clone wars held a bigger place in my mind. When the PT was announced, someone mentioned it should chronicle the clone wars, and I was on fire. The thought of that large scale, galactic battle with fighting jedi and space battles was very exciting for me. Like the space battle of Return of the Jedi on a larger and repeated scale.
The second was the thought of turning the original trilogy on its head. The OT was really about Luke, about his development, inner struggle, and eventual victory. If you went to that museum show of the Myth and Magic of Star Wars, they really delved into that angle. The whole Luke thing added a personal access point to the larger story of the rebellion and the empire. Vader, then, was a tool or an obstacle in Luke's development, something he had to face and overcome. As such, Vader supported the story of Luke.
With the PT, I realized that that would reverse, suddenly the focus would be on Vader, on his fall and redemption, and LUKE would become the tool and support to the story of VADER. Having what I consider one of the best told stories of cinema supporting a larger story, I thought, would provide layers of meaning and emotion and be quite an experience.
I watched the Episode I trailer and got quite excited. At the beginning of the crawl, I think that's the only time I've ever involuntarily screamed. I kept going back, looking for what I was expecting, figuring I had missed it somehow, but I never found it.