I used it quite happily circa 2009 and at a different company in 2014. In both cases it was being added to systems that already had mature functionality built a

I used it quite happily circa 2009 and at a different company in 2014. In both cases it was being added to systems that already had mature functionality built atop a RDBMS. In the first case it was used to store events that had started to overwhelm the main RDBMS with write volume. (Originally a system with one database as the monolithic data store.) Probably Kafka would have been even better for this use case, had Kafka been available at the time. But MongoDB did the job very well. I did a prototype in Cassandra too before settling on MongoDB, but MongoDB had much better docs, drivers, and single-node read performance at the time. The second time I used MongoDB to automatically track templated email bodies that were being delivered through a third party mail platform. We had dozens of recurring templates and many more one-off templates for different curated campaigns. If somebody complained that a link or image or token was wrong in their email, we wanted to be able to look back at the history to see if the problem was in the template data or potentially a client issue on their side. Most of the queries were ad-hoc and not very performance-sensitive. This was where a flexible JSON document format came in handy. Modern Postgres would have worked well for it too, but that wasn't available in the company at the time. With MongoDB I got good flexibility, adequate speed, and I avoided reinventing wheels by not trying to shoehorn the data into another MySQL table. I was able to solve a customer support pain point in less than a week and the system has worked well for nearly 4 years now. I'd be really frustrated if I had to use MongoDB as my only data store. I would guess that much of the hate for it comes from people who were forced into that position, or maybe from people who didn't take its documented limitations seriously enough before productionizing its use.