This episode was just honestly so good. I do think that they could have done a lot more with the crossover and involving some of this storyline within Supergirl and expanding on it so that parts of it didn’t feel rushed. I also love that the Music Meister ends up not really being a villain at all? He’s just teaching them a lesson about love - so the subplot about him using their powers was just shoved aside? That just felt a bit plot-hole-y and hand-wavy as did the whole him being called the Music Meister but the musical thing only happening because The Flash and Supergirl are into musicals? Still, I loved the episode and wish we just had more of it (which could have been done if they only used both hours to focus on this storyline). Also that last song that Barry sang to Iris was so amazing.