Have you heard Joss and his wife singing the songs from OMWF? It's no wonder James said he nearly shat himself with fear when he heard it (it's not that bad, but it really makes you realize how much the actors brought to the songs themselves). That episode is probably one of Joss's strongest writing-wise, but the actors, choreographers, vocal coaches, recording production, and costumers also really made that episode. Same with Dr. Horrible, which had the power to redeem Joss in my eyes, but then he literally followed his TV Trope:
"In some circles, the term "Jossed" refers to a gutwrenching main character death, which Joss Whedon is also famous for." - http://tvtropes.org/pmwiki/pmwiki.php/Main/Jossed