Osaka Castle and the surrounding park are a sight to behold. This was actually my third time visiting the park — I attended both Perfume FES 2017 and Kansai Lovers 2017 in September, but never ventured too far from the venues.
Finally, I made plans and returned to the park with just a camera and an afternoon. I wandered a bit (definitely not because I got lost) before reaching the castle, and was awestruck by the greenery and stonework around the moat. If that was the whole attraction, I would have left satisfied.
Reaching the castle itself, which is a small trek up a couple stone staircases, the exterior looks pristine for a castle of its age. It's both intimidating as it towers over you, but also notably small, as where it has height it lacks overall footprint.
Unfortunately, the exterior is really the high point. Inside is completely renovated and commercialized. Some of the display cases have what look like orignal items, but many of the displays are just recreations. There are many posters overflowing with text going into the history of all the wars, families, and battles this castle has seen and housed.
The very top floor, however, has been converted into a viewing deck overlooking the park, and does indeed let you appreciate the beauty of Osaka Castle Park. However what I can only assume are "suicide nets" prevent taking any reasonable photos, and are rather annoying obstructions.
After everything, I definitely would return to Osaka Castle Park just to walk around or relax, but probably wouldn't feel a need to return to the museum.