Could you at least watch a thing before calling it the worst?
I swear it's like a little kid saying he hates a food he's never tried.
Its a musical crossover on a fairly serious superhero show (and on one light sitcom starring Superman's cousin). Musical episodes are crap by default (with Buffy and Batman: TB&TB's episodes being the exceptions), and now its crap taking up one of the best shows on television (and Supergirl) for a whole week, with no legitimate way to justify it. So, yeah, this one gets heavily judged ahead of time. Musicals are crap, and have no place in a show like Flash.
I mean, I get why CW is doing it. The teen demographic of Glee is CW's bread and butter (at least with the majority of its non superhero shows), and I'm sure they aren't comfortable having superhero fans liking their network. That makes the decision make sense for them. As someone who is basically the complete opposite of the Glee demographic, this is just terrible. I've sat through horrible musical episodes before, and I never expected Flash to do it. Its a bit depressing to find that one of your favorite TV shows is having one less real episode, all because some idiots thought that High School Musical and Glee were good examples of how to make episodes of superhero shows.
What's next, an Arrow/LoT break dance crossover? Or maybe some other Flashverse actors have done crappy shows in the past that CW will want to rip off. Maybe a Law & Order episode of The Flash, basically a police procedural with the same characters but no superhumans? Or, maybe Slade will come back with a time machine and teleport everyone to ancient Rome? Then again, maybe Detective Lance has secretly been a wizard this whole time, and he'll save everyone with the help of his talking skull.
The rip offs of jobs the main casts have had will be a deep well to work from as the CW/Berlanti start taking the superheroics out of the DC shows and replacing them with terrible gimmicks that don't make any sense. Plus, some people will defend the choices and say they're justified because the actors once had a job on a show with a similar premise. I guess I need to apologize to Zach Snyder, he isn't the worst thing to happen to live action DC properties (just close to it).