[djur]

MongoDB isn't necessarily bad, but there's a number of valid reasons it's received a lot of bad publicity.

It was a high-profile representative of the NoSQL trend and that trend is experiencing a backlash. Since it has a relatively easy learning curve and a JavaScript-centric interface (JS also beng trendy), it got a lot more uptake by startups and inexperienced developers wanting to learn about NoSQL (or move away from the supposedly moribund relational model).

The ad-hoc querying makes it tempting to build object mappers around Mongo and write the kind of code you would with an ORM. A lot of NoSQL refugees did exactly that. You can get pretty far doing that before the caveats with that approach kick in. It's much harder to fall into that trap with something like Riak.

And then MongoDB itself has had some poorly chosen defaults and design decisions. These wouldn't be so high-profile if it wasn't for the other issues.