Trying to ascertain whether or not the best pop culture comes from Japan will depend on your own personal tastes. Ironically, a great deal of Japanese pop culture is influenced by American entertainment. That said, a great deal of the entertainment found in Japan is very unique and distinct. For those that have a love for many of the brilliant imports from Japan, there will be an assessment Japanese pop culture definitely is amazing.
J-Pop, despite the fact the songs are in Japanese, have a large following in other parts of the world. The huge success of Puffy Ami Yumi in the United States would be a perfect example of how music from Japan is welcome in the rest of the world.
Of course, any success of the Japanese music industry pales in comparison to the massive success of anime and manga in the US. Manga has overcome many American publishing companies in sales thanks to the huge customer base it draws from High School and Junior High School kids. Anime DVDs sell hugely among this market as well.
And yes, even the classic giant monster movies and television shows still have their fans and continue to sell to adults that grew up on this classic entertainment. Even as they grow into their adult years, these fans will still agree Japanese pop culture rules.