The audience for tokusatsu televesion was originally children, specificaly young boys. The shows have gone downhill in my opinion since the 1970s because the sponser, usually Bandai, had gained too much control and they changed who the core audience is, its now young women. The original Kamen Rider ran for 98 episodes. Goranger lasted 84. But Bandai couldn't sell enough toys when the shows didn't change every year so most tokusatsu tv got cut down to just a years worth of episodes On the other hand, a 1970s series could also get cut short if it dropped in the ratings, but later series were always a year no matter the ratings. If you look up the ratings they drop after the original series. The original Kamen Rider had the highest ratings. Goranger has the highest ratings for a sentai.
The special effects have gotten better, but plots and acting have gotten worse. I think a large part of the problem is they use younger actors. They actors pretending to be in their 20s in the 1970s were actually in their 30s and had previous acting experience. As for tjhe special effects I'll take black powder explosions and fireballs that you can see the wires holding up over CGI anyday.
Sentai means task force, its a military term and the originl sentai were military orginizations, they were also supposed to be international with the series just covering the local Japanese branch. The original Kamen Riders were cyborgs, part human, part machine. I don't know what the current ones are.
I find if I like the theme music I'll like the show and if I don't like the music I donn't usually care for the show it came from. I love the 70s theme music. Can't stand the current music.