I recently completed my first Camino (Norte, Primitivo, Finisterre/Muxia) and as high as my expectations were (especially after reading so many wonderful posts here on this Forum in the months before I left), I was surprised that actually doing it was even more amazing than anything I had read or any pictures or videos I had seen had prepared me for. All the answers here are great and really resonate with my experience.
I'd like to add one thing to this wonderful list that really surprised me since I don't consider myself a religious person and for me the experience was more of a spiritual journey. At some point deep into the Primitivo as I crossed a point with an amazing vista after hours of walking uphill, somehow my mind went to a movie I had last watched years ago, Chariots of Fire, and the line (which I remembered imperfectly at the time and have since looked up) the Eric Liddell character speaks: "When I run, I feel His pleasure". Liddell, of course, was speaking about his speed, but I felt so strong, the vista so awe-inspiring, my heart so full, I was surprised to find myself thinking, When I walk, I feel His glory.
I really hope to return for many Caminos, each of which I hope will be wonderful, but I suspect there is nothing like your first Camino (maybe a topic for another time?).
So enjoy every minute, feel gratitude for this gift, even when you're so tired you're not sure how you're going to manage those last kilometers or make it over that last hill (that first week starting with Irun will be hard! Stay open to the gifts the Camino offers and embrace all that surprises you!
Buen Camino!!