Replication is indeed not as advertised and neither is sharding. MongoDB hands off a lot of important details of the replica failover to the drivers which impl

Replication is indeed not as advertised and neither is sharding. MongoDB hands off a lot of important details of the replica failover to the drivers which implement them to varying degrees of quality. We had several instances where there was a node that was still up but had degraded network or other real life failure cases that were handled very badly causing the DB to become unavailable. The driver would attempt to contact the node on every connection due to it still being in the RS causing timeouts It handled a node becoming completely unreachable OK but that did not happen that often. I think they just added too many features too fast to get adopted widely. It appears now too they are less focused with improving the actual DB and more interested in getting in the enterprise services area. They market themselves as a general purpose DB but it is certainly not. I think many developers were turned on by the initial ease of use, and really did not consider if they should really be using a document store. We used it 100% due to the replication which does not work often.