The first 2 episodes are available online now: http://www.history.com/shows/the-world-wars/videos/trial-by-fire
My Grandfather was in WWI, and he wouldn't talk much about it either. He would talk a little about him having to stay in France recovering from injuries from a Mustard gas attack, and I once got out of him that he manned a machine gun for at least part of the time. He would never go into any detail about any of it. Later after my father died, we found some letters between him and my grandfather. My father was considering enlisting in the military for WWII (he eventually did) But all of the letters from my grandfather were telling(rather hinting) him that he didn't need to join, and that his advice was not to join if he could possibly help it. Of course after WWII my father didn't go into much detail about a lot of his experiences there either. He would talk about some things, but mostly he didn't talk about it.
A high school friend of mine is one of the executive producers. I've got it DVR'ed, but haven't watched it yet. Gonna go through in one go this weekend.
Sitting on the front porch of my wife's grandfather's house...listening to stories he had never told anyone ever before...was ridiculously humbling. The level of sacrifice those guys gave is so above and beyond anything I've ever remotely done in my life.