Why I like Power Rangers?
Well, I definitely have to agree with you about the general concept of the story: humans chosen to take on task of protecting Earth (and the entire galaxy for that matter), all the while taking care of other responsibilities outside of that job (school, work, relationships, etc etc). It's one of those stories that takes you into another world that consists of everything a person likes: adventure, action, fantasy, drama, mystery, and all that other good jazz that makes Power Rangers a fantastic franchise. Plus, like any other fan, I enjoy the martial arts, megazords (which happens to be a genius idea from the beginning- giant mechanical zords with extraordinary power), weapons, etc etc.
Power Rangers allows the viewer to escape out of the normal, and enter into a universe of imagination (much like Twilight Zone) Power Rangers is truly imagination at its best! Despite some seasons not being exactly what the fandom enjoyed, the fact that it lasted almost 20 years is historical in a sense. There's a ton of other potentially "greater" shows that got the can; and to know that a show that is targeted towards younger viewers lasts almost TWO DECADES is..indescribable to be honest. It's hard to describe how great a feeling that is. That pretty much sums up why I like Power Rangers.
