Interestingly, I was introduced to prog via metal. As a young teen, I listened to the usual heavy bands (e.g. Maiden, Priest). However, I always found their longer, more conceptual pieces more exciting than the straightforward 3-4 minute headbangers. I was particularly intrigued by Priest's "Victim of Changes" and "The Sentinel", while Maiden rocked my world with stuff like "To Tame a Land" and "Rime of the Ancient Mariner". At some point in the mid 80's, a friend literally forced me to borrow some of his Rush and Yes albums. My life changed then and there! It wasn't long before I made the startling discovered that Genesis was actually good at one time, and that Tull had much better albums than Aqualung.
Thanks for the question, Kazu. Ity brought back some great memories.
