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.
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.
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.
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.
Anyone realize how stupid it is for a character to be hated for being Blaster Happy?
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.