This is not meant as a troll post but a genuine observation after spending the last year or so migrating various businesses away from MongoDB (or from parse which uses mongo):

Has anyone ever built a non trivial application on MongoDB and been happy with their decision, say, 1 year later? If so, what kind of use case was it? I am genuinely curious.

The impression I've received is that Mongo is ridiculously easy to get started with but the flaws become more and more of a hindrance over time, eventually making certain types of application features virtually impossible to implement.