My opinion? I LOVE MD and i REALLY love WALK ON:
note... i love the popmart tour, but ending a show with ONE is like ending trainspotting without renton walking across the bridge as Underworld is playing. There is just no closure, no THIS IS THE END moment.
With 40 that exists, and it seems to me that as great and mindblowing as POPMART was, it just didn't have that last moment, that 8 minute closer. Walk On did that for me with the elevation tour. Granted, I love the Vertigo tour more and I love Popmart. But to me, Walk On is a great track, a perfect closer and because of that, I love Walk On.
That said, it has been done. It has a great solo and a great bridge. But I want Edge to rip into his guitar again and make me say, upon first listen "is that a guitar". That is something I can honestly say I haven't said (about the edge) since pop. I said it on Discotheque and Mofo, I said it on Some Days Are Better Than Others, and Love Is Blindness. And That is the sound, that strange otherworldliness that I want to return on the next album. And given what Rubin did on tracks like Animal Bar and Wet Sand and 21st Century and Death Of A Martian on Stadium Arcadium, he is the right man for the job.
The last time I said "is that a guitar" about a guitar was in reference to (of course) Tom Morello. And it was on an Audioslave track produced by Rick Rubin.
Is that a harmonica or a guitar?
When I hear MD and Walk On and Kite and even COBL I know I am hearing a guitar (there are a couple subtle moments on COBL where I am unsure, but i want full on confusion)...
and I want a new batch of songs that harkens back to that super futurist realm that edge created with tracks like Zooropa and Acrobat and Gone and Please. Man.... remember the first time you heard those songs?
Gob Bluth: "COME ON!"