I'd say that it's well and truly a children's show that assumes the children watching it are smart (which they usually are), nevertheless it should be entertaining to watch even to older audience. They will most likely appreciate the fact, that it doesn't have colourful, poppy presentation and pacing associated with Pokemon or similar.
For children, it's also interesting, fun, and exciting to watch. For adults, it doesn't have the repetitive storylines, plot holes and inconsistencies, stereotyped characters, or lack of ideas that one would normally associate with a "children's show". It was positively surprising to me, that thematics of it was sometimes mature enough to qualify it as entertaining even to mature audience.
It's a worthwhile anime. It's definitely better than some adult show you could mistake for children's if not for all fanservice included.
