This is a pretty nice park. There's more than just the sunsphere (which is awesome in its own right). But there are also green spaces, and fountains, and a playground on one end of the park. On the other end, there's a nice sidewalk that runs all the way down past the convention center, with a cool bridge to walk over and some more nice views of the sunsphere.
There's also an amphitheater where they sometimes have shows.
The only tough part is that there isn't a lot of parking nearby. It was a few minute walk from the lot when I finally found parking (up past the hotel and the playground)