Two young siblings are in the park enjoying a game of catch. One of them throws the ball too far and the other one runs off to retrieve it...only to return and find that the other sibling has vanished without a trace.
Bulk and Skull, the only original cast members left, had their popularity confirmed with their Crowning Moment of Awesome at the end of the season.
The Psycho Rangers, for giving Evil Counterparts to the Power Rangers that were finally characters with individual personalities and villains in their own right rather than just a cheap Evil Knock Off. Their sheer badassery also helped. They were popular enough to have a trope named after them. The fact that they were never made into action figures was a sore subject in some parts of the Ranger fandom... until it was announced at San Diego Comic-Con 2017, 18 years later, that action figures of the Psycho Rangers would finally be coming, as part of Bandai America's 6.5-inch Power Rangers Legacy Figures line.
Adam's appearance to help Carlos turned him into this.
Evil Is Sexy: Melody Perkins as Astronema gained quite a few fans from this series.
Fanon: The United Alliance of Evil being the name of the collection of Big Bads. It actually comes from a throwaway line in Power Rangers Zeo about King Mondo having broken away from something called the United Alliance of Evil - just who and what that is isn't expounded upon, and the name is never used at any other time. It makes a pretty good name for PRiS' villain group, but Canon it's not.
Also in most stories where Karone becomes a ranger as opposed to canon she will usually be the purple ranger based on the color of her honorary ranger outfit.
Fanon Discontinuity: "Shell Shocked", the crossover with Ninja Turtles: The Next Mutation is INFAMOUS among fans, mostly because of the other series - most choose to pretend the episode doesn't exist. The fact that the episode doesn't exactly connect with the third and the fifthnote while it does connect with the last scene in the third, other than that it's mostly stand-alone ("Shell Shocked" is the fourth episode) helps, so most choose to simply skip this episode.
Franchise Original Sin: This was the first series where the writers started doing straight forward adaptations of Sentai plots. However while Power Rangers in Space was content to simply adapting some filler episodes, otherwise telling a completely original story, succeeding seasons start to lean closer and closer to adapting Sentai plots and characters wholesale. This culminated in almost direct translation seasons like Power Rangers Wild Force and Power Rangers Samurai.
"Funny Aneurysm" Moment: "When Push Comes to Shove" and its 9/11 analogues. The episode featured Cassie and a guy she's on a date with trapped at the top of the tallest building in Angel Grove as a beast is trying to knock it to the ground, trying to send Angel Grove up in smoke.
Growing the Beard: Considered this for the franchise as a whole as this was when the series truly started telling serialized, season-long storytelling instead of just episodic plots with some isolated mini-arcs. Both heroes and villains started gaining more complex characterization, with villains (not Brainwashed and Crazy) that have the capacity for redemption and heroes that have flaws that are more than a Compressed Vice lasting a single episode and resolved with An Aesop.
For this particular series, the major storylines and dynamics of the season, such as the characterization that makes Ecliptor a fan-favorite, really all hit their stride once Darkonda shows up. There's a lot less filler from that point on.
Harsher in Hindsight: There is an entire episode that focus on Astronema using a monster to attack a building with people inside and cause it fall over. Of course this is Power Rangers so everyone survives, but imagine the writers trying to get this episode off the ground post 9/11.
Especially considering that this caused a whole lot of Power Rangers Time Force episodes to be re-edited and/or completely unaired when that series aired at about this time.
Astronema's "I wouldn't want to be a Power Ranger anyway!" Numerous production issues resulted in a post-reformation Karone becoming the Pink Ranger halfway through the next season. Even moreso in Super Megaforce's episode "Legendary Battle", the Extended Edition gives her this line: "I love being a Power Ranger..."
Kind of a meta example, but in the full version of the theme song there are the lyrics "Long live the Power Rangers." To elaborate. "In Space" was meant to be (and was in fact written as) the finale of Power Rangers as a franchise. This addition to the lyrics reflected this mindset, but if one looks at it from today and notices the 16+ seasons that followed...
Ho Yay: Andros has this with both Carlos and Zhane.
Iron Woobie: Andros; first his sister is abducted, then he and his best friend are the survivors of a supposed genocide, then said best friend takes a hit for him leaving him in cryostasis, leaving him alone on a spaceship for two years with only a sentient AI for company. That's a hell of a thing.
Les Yay: Ashley and Karone in the few scenes where Karone is Karone.
Narm: Andros crying on Astromena's body at the end of "Countdown To Destruction". The awfully obvious greenscreen doesn't help.
Dark Specter threatens to wipe out all life on Earth with a giant asteroid if the rangers don't turn Karone back over, and even after she's brainwashed, he lets the asteroid continue on its course anyways.
Aside from being responsible for the Barillian Bug infestation that made KO-35 abandoned, Darkonda kidnapped Karone as a child and when confronted by Andros, he refers to it as one of his greatest accomplishments.
Nightmare Fuel: Large Ham traits aside, there are moments after she's brainwashed that Astronema does come across as somewhat unnerving.
Her reveal in particular. We're used to seeing Astronema with a fairly rosy complexion and roughly a half-pound of glittery, shiny makeup, and she's very emotional, whether she's being sincere or hamming it up as a villain. When the chair spins around to reveal brainwashed Astronema, her face is ash-white, free of makeup, her voice entirely monotone, and her eyes completely devoid of any sort of humanity whatsoever.
On Andros's side of things: You're enjoying a simple day of playing ball with your little sister when she accidentally throws the ball too far. You run off to get it and when you get back, your sister is nowhere to be found. It's only later that you learn she was kidnapped...and you spend years thinking God knows what has happened to her and that it's all your fault.
Justin's return episode helped ebb a lot of the anger at his character, as despite everything he represented (an attempt to appeal to the kids), he was still a Ranger, a member of the team and there was some genuine emotion between all of them.
Most returning Rangers from Turbo are seen as that.
Rooting for the Empire: It's comical and minor, but who else was cheering on Rita during her fight with Divatox?
As with Ecliptor vs. Darkonda.
Also when Astronema kicks Darkonda out of the Dark Fortress, much to the delight of Ecliptor (as well as quite a handful of viewers).
She Really Can Act: While the Large Ham traits eventually resurfaced, the initial reveal of Karone being brainwashed was well done, with Melody Perkins being rather unnerving.
Ecliptor being killed by the Z Wave could count as this. Despite being created solely to be evil, he had shown a loyalty to Astromena, and was only evil in the finale due to being brainwashed by Dark Specter. Meanwhile, Zedd, Rita, and Divatox were purified by the Wave, with Rita going on to become, of all things, the Mystic Mother, despite them all having been shown as unrepentant in their villainy in previous seasons. Not only that, but what about Squatt, Baboo, Finster, Klank, Orbus and Porto- all of whom were not really villainous, so did they get turned human too or were they turned into sand as well? (Kinda justified, because that whole bit was imposed by the Fox Kids censors.)
Lokar would have been a perfect ally for the Ultimate Alliance of Evil, and a perfect weapon against the good guys. Upon the UAE's defeat, he would have likely been destroyed in a similar manner to his Zyuranger counterpart Dai-Satan.
They Wasted a Perfectly Good Plot: Despite numerous bits of foreshadowing, Dark Specter never finds out about Astronema's plan to drain his energy with the Psycho Rangers. It also never goes anywhere.
As per Christopher Khayman Lee himself, "Grandma Matchmaker" falls under this; he would've preferred Andros to be Ashley's "boyfriend" instead of Carlos.
It's debatable, but there are elements of this in the Psycho Ranger arc - the season had to that point been focused on the Rangers searching for Zordon and the massing armies of Dark Specter that consisted of all the Big Bads of the previous seasons, and then that all takes a backseat for eight episodes of a nearly beat-for-beat translation of the equivalent arc from Megaranger, keeping the Rangers mostly confined to Earth. While the Psycho Rangers delivered a storyline that fans had been waiting for since Rita unleashed the evil Green Ranger on the original Power Rangers, it did take away time from the ongoing storyline that this season had been building up to that point.
Tough Act to Follow: Every season after in Space has essentially been trying to copy the magic that made this season work. Some have managed better than others, but one major advantage this season has had over the others is the returning characters and strong mythology and continuity nods. The standalone team, standalone season format makes it more difficult to escalate the action and develop the characters.
Win Back the Crowd: Its predecessor, Turbo, has started to get some love for its second half, but is still widely considered a weak season overall by a lot of fans. In Space is still held in high regard and considered the best series by many.