After finding this thread and having my inner child suddenly hunger for Power Rangers I found myself looking a lot at the Super Sentai originals, mainly because everyone was claiming Power Rangers was nothing in comparison. But I can't really work out the difference, except for maybe some slightly better actors in the Japanese ones.
Super Sentais are very different from Power Rangers, despite the fact that some PR series chose to copy the plots literally from their sentai counterparts (like what PR Samurai is doing right now). Even in more goofy sentai series like the Go-onger, the Super Sentai franchise by and large have much better actors compared to Power Rangers, and the acting skills do make a difference since their performance won't distract you or take you out of the story. I also feel that Super Sentai have the better story, plot, and structure overall, and thanks to the cultural differences and the looser censorship in Japan, in a sentai series you can find more realistic violence and even death, and more sexual innuendos, than the Power Rangers would under Saban & Disney.
Is Power Rangers still a hit with kids? are the toys selling as well in the beginning? why is the show still on?
According to the Rangercrew board, the lattest episode "Fish Out of Water" for Power Rangers Samurai scored a 2.9, which is supposedly not that bad a rating. I'm not sure about the toy sales, however.
If you want to start off a sentai series to introduce you to this universe, I think Shinkenger (PR Samurai's counterpart) is an excellent start. Gokaiger is also terrific, because they henshin into past sentai teams and you can take a look at the history of the Super Sentai, and give you some general ideas on what they were all about.
Maybe I should check out one of the Super Sentai originals. Which is the best?
I would recommend Shinkenger, not because it is adapted by PR Samurai, but because this series' theme is samurai and the Japanese culture, you'll find it resonate alot better than what PR Samurai is doing. I think calling American actors Japanese feudal warriors, and put them in a pseudo-Japanese setting and lifestyle just don't make alot of sense. Other series that received high marks included Magiranger, Dekaranger, and Timeranger. Gokaiger (the most recent series) is amazing and you can follow it like rest of us do. If you want really old series, I'd recommend Dairanger, Jetman, and GoGoV.