I was struck by that too. When I was a teenager I thought Keats was pretty good, but I basically thought the human race had attained the peak of poetic possibility with John Lennon singing "I am the walrus goo goo g'joob." I didn't really know what it meant or what it was about, but more importantly, my parents didn't know either, and that made it unutterably cool. Somehow that "beyond my bourgeois parents' comprehension" factor doesn't seem so important anymore.

I still want mystery, though. I like "On the Cards and Dice," but I do think it loses some of its power once the riddle has been reduced to a rooster. It's tempting to interpret the poem as mocking a 17th Century version of "deep-image" poetry, but for me those images ("Whose very beard is flesh and mouth is horn") are too strong to be mere mockery.