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.
Complete Monster: Queen Bansheera is probably the worst boss in the history of the entire franchise. The queen of the demons, Bansheera returns to power by callously sucking the life out of one and forces Diabolico, her once loyal general, to open fire on his enemies without caring her most loyal minion Loki, whose only desire has ever been to serve her, is caught in the blast and dies. Diabolico has his mind forcibly erased to serve as her pawn. Her own son, Olympius fares little better, and Bansheera once ordered him abandoned to his fate while laughing. He is forced to fight alongside a brainwashed Diabolico, and his death provokes no feeling in her whatsoever. In addition, Bansheera attempts to open a gateway to the demon realm, allowing all demon-kind to pour out and overwhelm humanity.
Ensemble Darkhorse: Ryan. While it's per the course with The Sixth Ranger, he is special in that he is the first Ranger to not have a pre-existing Sentai counterpart. He was so popular, that he was near the finals in a Ranger popularity poll, there was a demand for a Titanium Ranger Key, and some have complained that he wasn't going to be in Super Megaforce.
There is also the theory that says that the Rescue Zords were built from or reverse-engineered from the wrecks of the original Rescue Zords. Supposedly, this was the writers' original plan, but nothing's ever been outright confirmed on the matter.
Fan-Preferred Couple: Carter and Dana. Some episodes suggest they are interested in each other and a flashback in "The Last Ranger" reveals the two are dating.
"Funny Aneurysm" Moment: Nearly every human-sized monster gets blown up, and Carter says "Mission Accomplished", except that Jinxer always brings them back to life and megazord-sized. Saying "Mission Accomplished" except the threat is far from over, and has actually gotten worse? Seems like President Bush's infamous 2003 moment, but "Lightspeed Rescue" aired in 2000.
Ho Yay: Absolutely obligatory for Carter and Ryan, being the Red and Sixth Rangers.
Same can be said for Joel and Chad in "The Mighty Mega-Battles".
On the Les Yay side, Kelsey/Nancy (from "Riding the Edge") has long been read this way by fans.
Moral Event Horizon: Queen Bansheera does truly horrible things. She crosses the line when Olympius, her son, ends up stuck in the local equivalent of Hell; she opts to leave him there for being useless enough to get stuck there in the first place, and seems to take perverse pleasure in doing it, too.
Never Live It Down: No matter how many badass moments Carter had, two things stick out amongst fans: using his blasters and his dull personality. For the former, this criticism was unfair in "Forever Red", where the Cogs he faced used blasters as well, and he was smart enough to use his own weapon.
Considering the Rangers function as a milita, the shoot first mentality made sense.
Mis-blamed: In regards to Carter, it's not his fault that his Sentai counterpart didn't use a sword. There weren't even any swords in the arsenal or toyline! Go Red used a gun, so the Red Lightspeed Ranger uses a gun.
So Okay, It's Average: Of all the Power Rangers seasons, this is probably the one which gets the most indifferent reaction from the fanbase. Very few actively dislike it in the same way that they do Turbo, Operation Overdrive or Samurai, but at the same time you likely won't find a single fan who considers it to be the show's best season.
They Wasted a Perfectly Good Plot: Dana is the Captain's daughter, she is the most knowledgeable of Lightspeed of the 5 Rangers. She is not chosen to be leader. Never once does the show actually address this issue or Dana feeling resentment or hurt. Mind you, Power Rangers Wild Force and Power Rangers S.P.D. would make the "Ranger more equipped to be leader, but isn't" into character plot points.
Not to mention, thanks to Linkara's review both Carter and the series' image overall is improved (though this started happening BEFORE Linkara's review). He points out how Carter Grayson may be dull but was a badass firefighter before being a ranger. While many fans disliked that Carter went for his guns first, Linkara loved that aspect because it made him one of the more Combat Pragmatist red rangers.
Visual Effects of Awesome: The Aquabase which was heavily detailed and built with an acutal aquarium to simulate the underwater environment.