“Glee” reunion. Raise your glass. (Adam Rose/FOX)

Fox’s “Glee” burst onto the scene in 2009; five years later, it barely made a blip on the pop culture radar as it celebrated its 100th episode. Perhaps sensing it’s not the groundbreaking force it used to be back in the day when it spawned an era of singing shows, the writers wisely took the opportunity to gaze back into the past at the glory days.

The network let viewers vote on songs from past seasons that they wanted to hear reinvented on Tuesday night’s 100th episode. Unsurprisingly, they’re all tunes from the show’s early days, when the storylines were at “slightly improbable” instead of “completely nonsensical.” The show managed to round up all the old cast members, even if they’ve moved on in real life: Rachel (Lea Michele); Mercedes (Amber Riley); Quinn (Dianna Agron); Brittany (Heather Morris); Santana (Naya Rivera); Puck (Mark Salling); Artie (Kevin McHale); Kurt (Chris Colfer); Blaine (Darren Criss); Becky (Lauren Potter) and Mike (Harry Shum Jr.).

And, of course, the grown-ups, including Sue Sylvester (Jane Lynch) and Will Schuester (Matthew Morrison) and special former guest stars April Rhodes (Kristin Chenoweth) and Holly Holliday (Gwyneth Paltrow). There was just a brief mention of Finn (Cory Monteith, who died last summer at age 31), as the characters remembered their friend.

Mostly, the plot centered around the fact that the glee club will finally be shutting down, thanks to the evil Sue Sylvester. Hmm … where have we heard that one before? In almost every single episode in the first two seasons? Anyway, since plot was never “Glee’s” strong suit, here’s every song they sang during the milestone episode (and video), and where it was originally heard in “Glee” lore.

“Raise Your Glass” (Pink) Video here

Originally performed: Season 2, Episode 16 (March 15, 2011) by the Warblers, the rival singing group
Excuse for bringing it back: Will Schuester, always a man with a plan, thinks former glee club star April Rhodes miiiight be able to save the  club — in any case, she arrives in the chorus room to sing a rousing rendition of the Pink hit to get everybody pumped up.
Better version: The remake. The adults looked adorably lame singing this one, with everyone’s glasses in the air: It had a certain spark that the Warblers lacked.

“Toxic” (Britney Spears) Video here

Originally performed: Season 2, Episode 2 (September 28, 2010) by the glee club and Mr. Schuester
Excuse for bringing it back: Former cool crowd members Santana, Brittany, Quinn reunite the old trio for a creepy version of this song, half the time in their old McKinley High cheerleading uniforms and half the time in burlesque-type outfits.
Better version: The original. That was the Britney Spears-centric episode, where Mr. Schue tries to look cool and join the kids on stage during a school assembly. As strange as that was, the real Britney made a cameo in the episode. That can’t be overlooked.

“Defying Gravity” (“Wicked” soundtrack) Video here

Originally performed: Season 1, Episode 9 (November 11, 2009) by Rachel and Kurt
Excuse for bringing it back: The first time around, Rachel and Kurt both auditioned to sing the song, known as a “diva off,” to decide who would get the solo. Kurt protested it shouldn’t automatically just go to Rachel because it’s a song traditionally performed by a woman; however, he ended up messing up the final high note. This time, Mercedes and Rachel are feuding about who is more successful post-high school — so they both belt this out (with some help from Kurt) so the glee club can vote on who is best. It’s very mature.
Better version: The original. Stakes were so much higher back then, and it was an actual emotional moment when Kurt made the mistake.

“Valerie” (The Zutons/Amy Winehouse) Video here

Original song: Season 2, Episode 9 (November 30, 2010) by Santana and the whole glee club
Excuse for bringing it back: After leaving high school, Brittany is apparently a lab rat at MIT where the scientists marvel at the weird way her brain works (remember, she famously said that dolphins are just gay sharks). She is also apparently a math genius. This makes her understandably sad, so Santana stages a remake of their old dance-centric song to cheer her up.
Better version: The remake. Such better dancing!

“Keep Holding On” (Avril Lavigne) Video here

Original song: Season 1, Episode 7 (October 14, 2009) by Finn, Rachel and the glee club
Excuse for bringing it back: Puck takes this on as an acoustic solo to woo back Quinn, his former love interest (and mother of his child) who is now dating a snobby rich guy named Biff McIntosh (Chace Crawford). Biff is amazing and Crawford shows off some surprisingly solid comedic chops — where was that talent on “Gossip Girl”? Anyway, Puck tries to win back Quinn (and ultimately succeeds) with a song that the glee club sang to her back in the day for support when she got pregnant.
Better version: The original. It’s truly haunting after Monteith’s death.


“Happy” (Gwyneth Paltrow)

Reprising her role as striving-to-be-cool Spanish teacher Holly Holliday, Paltrow showed up because why not? In the cliffhanger, she was apparently plotting with April Rhodes about how to save the glee club. But first, she had to perform Pharrell’s super-catchy Oscar-nominated hit.