IMHO the 70s was their best time, when Peter Gabriel stil had much influence in their music. Not to say that they didn't make any good songs with Collins, but it for me it got a bit too main stream then. And their success confirms this.
But their earlier works are simply epic, like music from Beethoven or Wagner. How much thought and skill went into it you quickly understand if you ever try to play that stuff on a keyboard or so.