A friend of mine actually had the concept of a Sentai based on classic movie monsters. Complete with secret base under a stereotypical gothic graveyard and other little touches we dreamed up just for fun. As I recall we had their mecha by the name of Terror-oh, or something similar.....
I think the concept was that while the team did have their powers and were good people, the rest of the world sees them as awful, perhaps because of what their predecessors did or just because of the motif. and your actual villainous group is perhaps some private agency that not only sends out the monsters, but spins the media so the Senshi are made out to be the villains and this company is fighting the good fight. Thus giving the main characters the tough decision of do they keep doing what they're doing and being good? Or do they follow the age-old creed of 'If you're going to call me a monster, I might as well act like one!'?
I think the concept was that while the team did have their powers and were good people, the rest of the world sees them as awful, perhaps because of what their predecessors did or just because of the motif. and your actual villainous group is perhaps some private agency that not only sends out the monsters, but spins the media so the Senshi are made out to be the villains and this company is fighting the good fight. Thus giving the main characters the tough decision of do they keep doing what they're doing and being good? Or do they follow the age-old creed of 'If you're going to call me a monster, I might as well act like one!'?