I think rocky and rooty is relative to where you're used to riding. I ride in very rocky and rooty conditions in the northeast so parts of KT feel super smooth to me. The good thing about KT is that there's something for everyone. There are trails that are predominantly made of sand, while others (like the ones on Burke Mountain) are filled with roots and other fun technical stuff. But, for the most part, the trails are fairly smooth and you won't have to manual over logs, etc.

You can go into the main office and tell them what kind of ride you're looking for and how long you want to be out. Chances are good that the person behind the counter helped build the trail and they're great at mapping out the perfect route for you. Plus, it's virtually impossible to get lost up there because everything is so well marked and the trails have a difficulty diamond rating too and even the black diamonds aren't too technical and difficult.