“The Substitute” is a weird episode. While the emphasis is on Holly Holiday, played by Gwyneth Paltrow, for good reason, it seemed like every other character was up to something or another, making the episode like a very loose collection of half-developed plots. The episode rolls along quickly and is actually quite good despite the numerous potential pitfalls.
The danger is that “The Substitute” becomes a personal showcase for Paltrow where the writers pile on an go overboard as they’ve done before. But although Paltrow shines spectacularly in both the songs, comedy, and drama, she doesn’t overwhelm the episode, due to Will balancing against her. They’re on opposite ends of the spectrum–Holly as the teacher who’s too fun and Will as the teacher who’s too strict. Both have their merits, but as teachers, not substitutes, a firm hand is needed sometimes. Will, who gets his job back in the end, balances their personality, asking for Holly’s help to make “Singin’ in the Rain” hip.
The aforementioned half-developed plots could actually work if they were the centerpiece of an episode. Unfortunately, they aren’t and the plots jump around without much development. There’s Rachel vs. Holly for a while before Holly teaches Rachel an important lesson, Sue being principal and getting rid of Will before hiring him back, Kurt and Blaine hanging up while Mercedes gets shafted, eventually realizing she needs to find someone of her own, the bully at it again. And lastly there’s the return of Terri who randomly shows up to take care of Will. I have no clue why, because by the end of the episode she’s gone, hopefully written off forever by both Will and the writers.