I saw a band (not U2) play five shows in five nights last year and being a big fan of the band I enjoyed every single show. That said, not every one of those shows was stellar. Two were fantastic -- every band member having a great night and really playing off each other and the crowd wonderfully. One was very good, but had a few problems and didn't quite have the magic of the first two I mentioned (it was the first time I'd ever seen this band live, so it holds a special place for me anyway).
One show -- the last of the five I saw -- was in a poor venue with horrid sound and no sound check because the bands were late in arriving that day (a couple hundred miles of near blizzard conditions to drive through). And trust me it sounded as if they had no sound check, especially for the first several songs. They did give as good a show as they could under the circumstances, but with all the problems they had (they were all sick and very tired as well), objectively it couldn't be considered a great show.
And one show, which I enjoyed a whole lot, really couldn't objectively be called a success at all. One band member had technical difficulties throughout the night and became increasingly surly, finally walking offstage and leaving the venue. That pretty much ended that show. I enjoyed the banter from the other band members (and getting to talk to one for quite a while after the show
), but I know I would have been really disappointed if it had been my only show.
My point, however, is that with a band you adore, you can enjoy every show, even if it isn't one of their very best ones. But also as fans of these bands we have to realise that not everyone adores the bands we love, and sometimes they will notice and comment on errors/problems we are more apt to find charming.
Not every show is going to be utterly fantastic, but most shows do offer fans very enjoyable experiences. If you had a good time, don't worry what others think.