These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Deconstruction Fic: A great deal of Power Rangers fanfic (especially with the original characters) portrays the characters as if the constant power losses, mind hijackings, and secrecy actually had the profound psychological effects one would expect these sort of things to have on a teenager. One of the more well known Mighty Morphin' era fics, Personality Conflicts, starts with Tommy entering psychotherapy.
Dork Age: Turbo and Bruce Kalish's run on the show, SPD through Jungle Fury, tend to be considered this. Also a specific period during season 2 of Mighty Morphin' after Jason, Zack and Trini's actors left the show, before their characters leave ("Power Transfer II"), because their characters were in the show but only using stock footage and while morphed using bad dubbers for their dialog.
Ensemble Darkhorse: Tommy wasn't even slated to return due to his Sentai counterpart dying (lack of Sentai footage and all). But the character's popularity made the producers request for TOEI to use them in their additional footage shot exclusively for Power Ranger and then they brought him back as the White Ranger AND the leader of the Power Rangers when that footage of the Green Ran bled dry.
The reunion/team-up special "Once A Ranger" embodied this with it's usage of fan favorite characters Bridge Carson and Adam Park. Bridge was given a color upgrade to Red SPD Ranger to justify his character's return (since the two-parter also had the Mystic Force Green Ranger and the Ninja Storm Blue Ranger) while Adam (the Black Ranger) was appointed team leader of the group of inactive Rangers summoned to help out the Overdrive Rangers.
Bulk and Skull could probably qualify. They were entirely one-dimensional in the first season but got personalities and more screen time from the second season onward, culminating in them leading an "I am Spartacus" charge against the In Space big bad when she demanded that the people of Earth turn over the Power Rangers to her to kill.
Heck, the first Power Morphicon had a panel called "Unsung Heroes", which was nothing but Ensemble Darkhorses and featured many of the above characters.
There seems to be something of an unintentional tradition that Green Rangers almost always become Ensemble Darkhorses. Starting with original Green Ranger Tommy and Adam from Zeo and Turbo all the way up to Mike from Samurai, even if a season is pretty lackluster, the Green Rangers are almost always pretty well-liked (Bridge, Xander, Ziggy, etc.)
Evil Is Sexy: Played with in the earlier seasons, but it wasn't until In Space's Astronema that it took complete hold. Now every season there is at least one attractive humanoid evil female who most of the time fights the good guys.
Fan Nickname: The Japanese recorded action sequences from the end of the first season (Starting with Something Fishy and every episode after Crystal of Nightmares) and the first half of the second season (until "Missing Green", before they began using Dairanger monsters on the show) is dubbed Zyu2 in fan circles, due to the fact that they were recorded specifically for Mighty Morphin Power Rangers and were not from any actual Zyuranger episodes.
Fanon: Due to every Power Rangers series other than RPM being in the same universe and the fact that many elements or other occurrences in the show aren't officially explained, this happens a lot. There's even more when one considers things that were once going to be official explanations, but were later taken out for one reason or another, such as the Lightspeed Aquabase being built from old destroyed Zords, Billy having developed the Turbo morphers during Zeo and the Great Offscreen War three thousand years ago mentioned in Lost Galaxy and Wild Force being the same event, indicating that the Galactabeasts and the Wildzords are connected.
First Installment Wins: Mighty Morphin' was an instant hit, and became a major phenomenon, on par with Teenage Mutant Ninja Turtles a few years earlier and Pokemon a few years later. The sequel series couldn't possibly keep up that momentum, and Mighty Morphin' is far and away the best remembered installment, and the one that the average person is referring to when they say simply Power Rangers.
It Gets Better: Most Power Rangers series start off with filler (often AesopOf The Week type episodes), but pretty much all seasons hit their stride a few episodes in, once the first major story arc occurs.
Macekre: While chopping up the Sentai episodes is common, season 3 of the original show really has to take the cake. In Kakuranger, the robots which would become the Shogunzords appeared first, with the proto-Ninjazords as the Mid-Season Upgrade. Saban flipped it around since the larger, humanoid Shogunzords would seem more natural as upgrades. The best example: the first Monster of the Week in season 3, Vampirus, comes from episode 36 of Kakuranger. And let's not get into Zyu2 and Dairanger...
The seasons with Tommy are the best Power Ranger shows.
The seasons up to in Space are the best Power Ranger shows.
Only Power Rangers of the Saban era (anything up until Time Force) are the best Power Rangers shows.
Only Power Rangers made by the original production team (until Wild Force) are the best Power Rangers shows. Notable because the current executive producer, Johnathan Tzachor (who held the same title with MMPR Productions), is a member of this camp.
Only Power Rangers before Bruce Kalish became Executive Producer (up to and including Dino Thunder) are the best Power Ranger shows.
Same as above but including Bruce Kalish's first season (SPD) are the best Power Ranger shows.
Same as above but including the final Disney season, and the first without Bruce Kalish (RPM) are the best Power Ranger shows.
Periphery Demographic: The show has a staggering amount of adult fans for a kids' show. This is probably because most of the current adult fans were children when it first ran.
Johnny Yong Bosch (Adam, the second Black Ranger and Green Zeo Ranger) is very well known in the anime dubbing community, especially as Vash from Trigun, Ichigo from Bleach, and Lelouch from Code Geass.
So Bad, It's Good: Before In Space, it was almost universally considered the only reason anybody watched it. It has since gotten better, but its overall cheesy charm means that this trope still stands.
They Just Didn't Care: Disney's perceived attitude towards the series, at least during the later Disney seasons.
This is actually why Saban bought the rights back. Disney didn't really embrace the Power Rangers franchise due to the perceived violence... then they went and purchased Marvel Comics, which has far more violent characters.
Under Disney, the toyline also fell from the top Boys Toys spot for the first time in literally a decade. While the Transformers film toyline was a major cause, cost-cutting measures meant new, cheaper and often inferior Megazord toys, which are the main drive of the toyline. Half of the RPM toyline never even reached America!
They Wasted a Perfectly Good Plot: With the Gokaiger footage coinciding with the series' 20th anniversary, you'd think it would make sense to go from Super Samurai straight into that. Unfortunately, Saban was contractually obligated not to skip any Super Sentai series, and Nickelodeon had messed things up by halving the number of episodes in a season, forcing Saban to split the Shinkenger adaptation over two years. The best Saban could do at that point was to merge Goseiger and Gokaiger into one story, so that Gokaiger is at least closely related to the anniversary.
Surprisingly Improved Sequel: A case could be made for the early seasons, as the show went from an almost plotless beat-em-up to... well, having plot.
Unfortunate Implications: The original Black Ranger was black, and the original Yellow Ranger was Asian. (To be fair, the producers did not realize what they had accidentally done until several episodes in, when it was too late to change anything.) Their replacements' races were flipped to fix this while preserving the Five-Token Band, and the franchise didn't cast another black Black Ranger until Operation Overdrive's Will. While we're on the subject, Will was a professional thief.
Then there was the writers' later decision to stress Tommy's Native American heritage. Anyone remember what color he was in Zeo and Turbo?
No one brings up Dominic and Udonna who were Caucasian White Rangers.
The casting sheet for Samurai originally listed that the characters can be of any ethnicity...except for the Red Ranger, who had to be white. Considering just how many white samurai there were in Japan, um... (They changed it to "all ethnicities", but cast a white guy as Red anyway.)
And, as has been confirmed the actress that will be the second Red Samurai Ranger is also white, well...
Justified as the two Red Rangers are siblings, making keeping the race consistent is kind of important.
As of Megaforce, the "only one black person per team, but no limits on white or apparently-white people" dynamic is starting to come under serious scrutiny after an incident where an actress was apparently told this was the reason they wouldn't cast her.
Warped Aesop: Power Rangers has always had a heavy emphasis on teamwork and how important it is. Every person in the group has something to contribute and is invaluable...as long as you're either the Red Ranger or the Sixth Ranger. This doesn't apply to every season, but there's more than a few where the Red Ranger completely hogs the spotlight and the other rangers are really there just to be his cheerleaders.
Win Back The Crowd: Both in Space and RPM, fan-favorites considered some of the franchise's best, which followed Turbo and Bruce Kalish's run, respectively, which... aren't.