It's been several years (and the issues are in my office so I could take a look later) but I recall it was a mix. They'd sometimes group big stories together thematically (like when all the billionaires were starting to get into space) but also do longer-term reflections on single, complex stories like the Salisbury Novichok incident.

I don't recall it really surfacing things that didn't make the news cycle, but one thing I failed to mention is they had (have?) really good infographics/visualizations! They have a lot of the more recent ones here https://www.slow-journalism.com/filter/infographics