The special effects, and the characters.
Compared to America, the Japanese have more imagination.
Since I was a kid, I loved Godzilla films, kaijuu eiga, and all sorts of Japanese sci-fi.
The special effects were colorful, spectacular, and imaginative. Whether it's giant monsters smashing cities, alien invaders trying to conquer Earth, or superheroes fighting mutants, demons, and mad scientists,
Godzilla, Gamera, King Ghidorah, Gomora and many other monsters all looked and felt real. And they had memorable designs and great personalities. Godzilla turned from a villain, to a reluctant antihero, to an anthropomorphic superhero in the original series of films. Whereas Gamera, despite his initial violent personality, was misunderstood before becoming a childrens' hero. These monsters are gods! How many American monsters can you find like these?
Superhero adventures were everything American movies & TV shows wish they could be. You have colorful superheroes fighting supervillains, monsters, and other threats, just like in a comic-book. In fact, they were live-action comic-books! No matter how "cheesy" the FX were, they always try to visualize something spectacular. If Toei's version of Spider-Man were 100% faithful to the comics, Green Goblin could be flying on his Goblin Glider, via either miniature FX or bluescreen. Something Americans would never have allowed, because they were more concerned with absolute realism (and companies were desperately trying to shy away from the "campiness" of the 60s Batman series, which was true to the comics). Ultraman was a new superhero concept; a mysterious alien creature who comes to Earth to protect it from threats like giant monsters and sinister aliens. (In a way, Ultraman himself was like a giant monster, like the ones he fought; he's giant-sized, rarely speaks, and always says "Shuwatch!") Ultra Seven carried the Ultraman formula further, giving the titular hero more audience empathy, and the series a strong sci-fi drama! And, of course, you have the many memorable giant monsters from the series.
In all cases, there's also the fascination with miniature FX, and miniatures in general. Japanese studios such as Toho, Tsuburaya and others have built beautiful, colorful and detailed miniatures of Tokyo and other Japanese locales. There was so much craftsmanship put into these works, and CGI can never truly replace this effect. If done realistically, these miniature sets work great with the suitmation monster walking through them, or any other sort of disaster (natural, alien, etc.).
And then, you have the mecha fascination. There's plenty of vehicles (like Atragon, the Ultra-Hawk, or Moonlight SY-3), weapons (the Maser Tanks), and even giant robots (Giant Robo, Red Baron, Battle Fever Robo, Dyna Robo, etc.). Japan has had a long-standing fascination with machines, leading to the collecting of toys and model kits. This can apply to anime as well.
And these are among the things that attract me to tokusatsu.