I've never been to Colorado, but I've gone from KC to Oklahoma, and if it's anything comparable it's a very nice drive--lots of flatland without much breaking up the scenery, which I found very relaxing. I guess you'd get some more highland as you get up towards Colorado, though--that'd be nice to see, I bet.
Though it was a long trip across there, when we had the double nickel speed limit, sheesh, Kansas and eastern Colorado went on forever.