There's old Genesis and new Genesis. I think the old songs have much more musical imagination, not to mention Gabriel's fascinating voice. Many are more like compostions than songs, too.
"Selling England by the Pound" is my favorite studio LP. Get that one, but also get "Seconds Out", excellent live renditions of many of the greatest ones. Plus, the drumwork by Chester Thompson and Bill Bruford (and Phil, of course) is something to hear.
Best Yes album: Close to the Edge (I couldn't resist).
Steve O.