Osaka Castle is a beautiful historical site with a great atmosphere, and visiting the observation deck at the top is definitely worth it for the wonderful city view. I would really recommend booking tickets online in advance, because the queue for buying tickets on the spot can be quite long, especially on weekends or holidays.
Inside the castle, it can get quite crowded and the stairways going up and down are narrow, so it may feel a bit packed at times. Also, please note that there are some floors (like the 2nd and 3rd floors) where photography is not allowed, which might be disappointing for those who want to capture every part of the experience.
One thing that could be improved is that there’s no priority route for elderly visitors, so the stairs and crowd can be a bit challenging for them.
Overall, it’s still a memorable visit with a great view and a strong sense of history — just be prepared for the crowds and plan ahead by reserving tickets online.