MMPR was extremely cheesy and yet somehow managed to work quite well and ranks way above most of the rest, with only tough competition from Zeo & In Space. One of my absolute favourite episodes from MMPR, from the 3rd season (Wizard for a Day), where they basically make fun of the entire premise of the series, right down to the stupidity of trying to conquer a planet by sending down monsters that always get defeated. That episode was hilarious all the way through.
Season 1 was cheap, with tiny bits of cheaply produced US footage badly tacked on to stock Japanese footage. It's episodic approach was corny & melodramatic, but the characters stood out and ultimately S1's biggest saving grace being the introduction of the Green Ranger. The 5-parter "Green With Evil", is where S1 truly began to shine.
Season 2 was much less cheap and took a stab at being a little bit more serious to begin with, yet still retaining the cheese factor that made it so popular. Lord Zedd was a much more interesting & darker villain than Rita and in S2 they made more effort towards creating a loose storyline. Losing 3 of the cast did hurt the show a bit, but they made up for it. The return of Rita towards the end was both fantastic & hilarious.
I'm probably in the minority here who actually loved Season 3. They did get cheap again a bit, particularly referring to those ninja costumes which allowed suit actors to do all the stunts and fighting. But S3's plot threads were quite strong, with lots of multi-part stories. I even enjoyed the Alien Rangers stuff. I also didn't mind too much them turning Lord Zedd into a comedic villain by this point. Silly antics worked quite well for this series as a whole.