Alright, so arguably my opinion is worthless, since the only other bands I've seen besides U2 are Weezer and Todd Rudgren (with some other famous musicians, including John Entwhistle! dunno how to spell his name, but the bassist for The Who). But I've watched DVDs, heard experiences, listened to recordings... and for me, NOTHING can touch U2. Allow me to give you a horrible example that will make you all cringe and throw sharp objects at me...
I was listening to Linkin Park: Live in Texas, and during the song "Crawling" the singer guy kept trying to get everyone to sing along... he wanted the audience to sing it, which I thought was cool. However, I found myself laughing (and yes, I do like Linkin Park, get the hell over it). Perhaps it was just the mixing, but even after much prompting the audience was barely audible, and the singer kept having to go "I can't hear you! Sing it now!" or whatever. Let's compare this to a U2 concert... the audience is singing along for the ENTIRE concert, listen to bootlegs and you can clearly hear the audience. One of the most noticable parts is The Fly...Bono singing over what sounds like a beautiful choir of "Love...we shine like a burning star..." The audience sounds INCREDIBLE. Or in One - Bono will sometimes stop at "...got someone to blame, well it's - " and let the audience sing "too late tonight to drag the past out into the light." Does he have to TELL the audience to sing? HELL no! If Bono for whatever reason stops singing, the audience will sing for him. Often times the audience will start the "woohoo's" in Elevation before Bono does, and of course there's the 40 chant. It's all about audience interaction and unity... when you go to a U2 concert, you're not going to watch a band perform. You are a part of the concert, a part of something much bigger than yourself. To me, that says miles more than setlist length or variation or whatever, and even the musicianship (though many people will disagree, I'd say U2 is generally pretty tight...because of their minimalist style, paticulary Edge, when they do make a mistake it is very noticable, and of course Bono messes up lyrics sometimes, but overall I'd say they are very professional and rarely sloppy.) Another thing that makes U2 shine - they NAIL their songs live, and so many songs become bigger and better. U2 in the studio is genius, U2 live is something else entirely... I mean, honestly, I'm just speaking for myself here, but once I've heard a U2 song live, it's hard for me to go back to the album version. Please, Bad, The Fly, Streets, Sometimes, Sunday Bloody Sunday... all songs that were brilliantly recorded, but I hardly listen to them anymore. I listen to live versions.
Of couse there are other things that make U2 live great, such as the stage lighting and concepts and all that (ZooTV is probably one of the best things ever), but in the end it's all about the passion...the band really give it their all, and so does the audience! There's a connection between band and audience that I think is rare... of course there's the pulling up of fans on stage and all that (to play guitar no less!), but it's also just the little things... the way Bono's always interacting with the crowd, and now even Adam is getting a taste of it... and of course the way the audience makes itself a part of the show. Strange as it may seem, I think the best part of my Vertigo show was when the band had left the stage... the entire audience was singing, "How long to sing this song?" and we even started a synchronized clap...it was truly incredible, and I felt like I was truly a part of something. It's something so fucking beautiful that can't truly be understood until you experience it yourself, but to me that sums up U2 live. The unity. Passion and unity, those are the two main things... a U2 show isn't a show, it's an experience.
Are you FREAKING 
?????
I've always considered Tool to be the U2 of heavy metal in terms of musical quality, passion, diversity, and emotion... Tool 
