It has been a subject of debate amongst fans whether if Power Rangers seasons that are faithful to their Sentai counterparts are good or not. Let's take a look:
Power Rangers in Space (Psycho Rangers Arc)
While the first five seasons of Power Rangers, as well as Power Rangers in Space were indeed original, the only part of Power Rangers in Space that copied from Megaranger was the Psycho Rangers arc. The plots were very similar to the Nejiranger arc episodes, with only some differences here and there. During the time that this was airing, most fans did not know about Super Sentai, thus not many people made comparisons. Most fans loved the Psycho Rangers arc, as it was something that fans had always wanted from Power Rangers. I'm kinda surprised that something like this hasn't been re-done in either Super Sentai or Power Rangers. But anyway, the only minor criticism that this arc tends to receive is that the whole story came to a halt, just to focus on this arc.
Power Rangers Lost Galaxy
Indeed, Power Rangers Lost Galaxy had a completely different motif from it's Sentai counterpart, Gingaman. However, if looked closely, 2/3 of Lost Galaxy's story is copied off from Gingaman's story. In fact, many scenes were copied word for word. Many fans often criticize Lost Galaxy, saying that Gingaman's scripts did not work well with the Space Colony motif. There were several scenes where the Lost Galaxy characters would start talking about something nature related (Gingaman's motif), which lead to many awkward and random looking scenes. Fans often say that Lost Galaxy was at it's best when it was original, and that for 2/3 of the season, the story halted just for the sake of using up Gingaman footage. The only scenes that were actually re-written the most were the Magna Defender scenes. While Magna Defender's story is very similar to BullBlack's story, there are some key differences in the plot and dialogue, which can slightly give off a different experience. Something that the fans have indeed praised. Overall, fans are divided over whether Lost Galaxy did an okay job or not with handling Gingaman's footage.
Power Rangers Lightspeed Rescue
This was the very first season that was noticeably much more faithful to it's sentai counterpart. Even though most fans weren't aware of Super Sentai when this show was airing, today, Super Sentai plays a huge role in people's views on this season. When Lightspeed Rescue was still airing, fans were very divided on this season. And to this day, fans still are, to the point where this season is most definitely underrated. Lightspeed Rescue had some pretty good actors and characterizations in the show. Not to mention that the plots were actually pretty good. The only major weaknesses of this season would've been the villains and the pacing of the plot. Going back to the topic of "Faithful Adaptations," Lightspeed Rescue picks up the rescue motif that GoGoFive had. And it also copied certain plot points like Queen Bansheera arriving on Earth. But what made Lightspeed Rescue different from GoGoFive was that it created it's own individual stories by working around GoGoFive's existing footage. And thanks to sharing the same rescue motif, it worked pretty well. Plus, Lightspeed Rescue managed to squeeze in it's own original Titanium Ranger. Another major element that made Lightspeed Rescue different from GoGoFive was the lack of the family theme (which was the main driving force for GoGoFive). Comparing Lightspeed Rescue's work with the Sentai footage compared to Lost Galaxy's, there's a huge noticeable improvement. And I think this is something that the show deserves lots of credit for.
Power Rangers Time Force
Even though Lightspeed Rescue did a good job with the Sentai footage, it still had a lot of problems concerning it's overall story and characters. To many fans, Power Rangers Time Force was "THE perfection" of Power Rangers. It had strong powerful characters, great villains, exceptionally good acting, a much darker and grittier atmosphere, and an overall intense storyline. Like Lightspeed Rescue before it, most fans weren't aware of Super Sentai when this show was airing (though by this time, more fans started to get aware). Today, since most fans are aware of Super Sentai, many fans kind of view Time Force as a watered down version of Timeranger, due to how closely the plots were copied, while not being as powerful. Regardless, Time Force already received a good number of fans who are now nostalgic for this season, and is considered a classic. Despite Time Force pretty much copying Timeranger's plots, like Lightspeed Rescue, it does a rather excellent job at working with the source material, while still making the dialogue original. Many fans praise Time Force's scripts for being very well written.
Power Rangers Wild Force
Unlike the last couple of seasons, one of Wild Force's biggest criticisms is that it copied Gaoranger word for word. Thus, there wasn't much originality in the scripts or the handling of the source material like Lightspeed Rescue and Time Force attempted. It just became a copy of Gaoranger, which happened to be very watered down. Most fans blame it on the poor below par acting for this season.
Power Rangers Ninja Storm
Once again, the plots for this season were very similar to it's Sentai counterpart, Hurricaneger. But unlike Wild Force, Ninja Storm didn't copy the scripts word for word. The scripts were more original, and leaned in more towards the parody style like Carranger. Thus, most fans often ignore the handling of the source material and instead decide whether the comedy is the right style for them or not.
Power Rangers SPD
During the early episodes, Power Rangers SPD would work around Dekaranger's footage and try to create original dialogue to help develop the SPD cast. Unfortunately, Power Rangers SPD took a turn for the worse and started to copy Dekaranger's scripts word for word, while still being watered down compared to Dekaranger.
Power Rangers Mystic Force
This season has also been criticized for blatantly copying Magiranger's scripts so closely. Though a major difference would be that any cheesy scenes from Magiranger would be cut out. Fans felt this season was just merely a watered down version of Magiranger. The only slight bit of praise that this season ever receives is whenever it tries to be original.
Power Rangers Operation Overdrive
This season tried to be more original at the start, but failed very quickly. Once again, just blatantly copying Sentai's scripts and mixing it up with terrible acting and plot pacing. Not even the whole Mack being a cyborg plot made things any better. The show was a complete mess.
Power Rangers Jungle Fury
This season was another season that pretty much copied it's Sentai counterpart's plots. But like Lightspeed Rescue, Time Force, and Ninja Storm before it, Jungle Fury attempted to make more original plots while working around Gekiranger's footage, as well as making original dialogue. And frankly, the dialogue for this season was actually quite good. And it got even better as the season progressed. And like Lightspeed Rescue, Jungle Fury managed to bring in their own three original rangers, the Spirit Rangers into the story. The characters however were average, but were still passable. Most fans tend to lump Jungle Fury up with the other Kalish seasons, but I personally don't think this season is THAT bad. Like Lightspeed Rescue, I think it's rather underrated and much better than what fans keep making it out to be.
Power Rangers Samurai
According to the information released so far, Power Rangers Samurai is expected to be a faithful adaptation of Shinkenger, with Jonathan Tzachor as the head producer. We'll soon find out if this season can do a good job with it or not. I personally of course would much rather see a completely original story rather than a re-telling of an already existing story, but oh well. I suppose the most I can do is watch and see if it handles the footage properly.