Some people felt disappointed and said that Natsu-iro Kiseki wasted the potential from its premise: like, you have a wishes-granting rock but you don't use it to do 'amazing things', and the rock itself does not always work exactly like you have expected, either.
- Okay, so anime viewers, you haven't been bored by the trope "an interesting plot with an easy-to-use wishes-granting power", have you?
When I was a kid, I spent much time watching Doraemon (you know? it's one of the legendary manga/anime, The longest-beloved kid M/A) and I've got enough with that trope.
So I'm glad that Natsu-iro Kiseki didn't follow that old trope, instead the wishes-granting rock here seems more like a mature friend who provides the necessary helps for our four middle school girls to realize some precious things in life, and grow up themselves.
Another hightlight is that it doesn't feel like a surreal anime, the characters are extremely realistic. They don't need to show off their cuteness to make me love them.
Now you see the point. No wonder many reviewers give this show high scores with praises. You should read their reviews if you're still hesitating.
I am Vietnamese and not excellent at English so I couldn't write a long and detailed review. Sorry for that. =))