I find this article to be more a reflection of a NoSQL newbie's failed foray with a document database that later realized that the grass is not as green as originally perceived. The developer realized that he does not like map-reduce and missed not having joins. I don't see how this person's failed experience with MongoDB is a reflection on MongoDB.
I think the recent popularity of MongoDB bashing is maybe a testament to MongoDBs popularity. I'd guess that because MongoDB is probably the closest NoSQL database to a RDBMS with its ad hoc queries, that it is attracting many newcomers.
Yes, MongoDB is more of a general-purpose database with lots of features that remind us of relational databases. It is a purpose-built application database for applications that would otherwise almost certainly be built with a relational database. As they get deeper into their project and find out how some of the trade-offs play-out their self-doubt is always about "should we just go relational" - no one is staying up all night wondering if they should migrate to Riak. If you start out with Riak you almost certainly know why and are using it in a very specific context.
I think the recent popularity of MongoDB bashing is maybe a testament to MongoDBs popularity. I'd guess that because MongoDB is probably the closest NoSQL database to a RDBMS with its ad hoc queries, that it is attracting many newcomers.