After seeing several original Japanese castles, we decided to skip Osaka Castle even though it's one of the city's biggest landmarks. While impressive from the outside - those massive stone walls and golden accents are pretty spectacular - the inside is a modern concrete reconstruction with a museum rather than an authentic castle interior.
That said, the grounds are stunning, especially during cherry blossom season when the entire park turns pink. The castle's significance in Japanese history is huge - Toyotomi Hideyoshi built it in 1583 as what was supposed to be the center of a unified Japan. Even if the current structure is a reconstruction, those original stone walls tell stories of sieges and samurai battles.