The boringness due to long run time isn't because people have short attention spans - it's because it is literally one act stretched over two by covering everything twice, once in spoken/visual and then again in song. As a theater fan, I am happy the musical numbers were cut minimally, but I was annoyed by their constant stop-start with dialogue often explaining what is already said in the songs. It also made the plot less interesting as it only covered half the talking points in the time it could have covered the whole show. Reading other critiques, it seems some people had a hard time following the plot and the only thing I can imagine is it was too slow, too in their face, and importantly only half the story!
All these big budget movies with everything happening in every single shot can be a bit too intense to watch. Maybe I'm just a theater kid, but Idina and Christins cameo just made me think they could have done their own roles in a much simplermovie and I would have been much happier.