Great blogpost on Kansas from last April complete with a link to a live recording of a 70s concert which I've never heard before. Money quote:
The dual heavy guitar attack of Kerry Livgren & Rich Williams blended with singer Steve Walsh's keys and there was also the lead violin of Robby Steinhardt. While the intricate melodies and odd time signatures certainly put them in the same category as Genesis and Yes, Kansas had a very different flavor. I've always thought of them as being the Aaron Copeland of progressive rock. A song like "Cheyenne Anthem", dealing with the Native American tribe, could never have been done by any of the prog heavyweights across The Pond, for instance.
One thing I like about Kansas is they weren't just a second rate "rip off" of the British prog rockers who created this genre, but rather mixed in a strong element of "Americana" (hence the Aaron Copeland comparison) that was absent from British prog rock.