At YAPC::NA 2015, I gave a talk comparing MongoDB to Perl as another Swiss-Army chainsaw. This year, I'll give a chronology of changes that make MongoDB less likely to take your leg off.
33. 2016-2017
no '.' in @INC
ref-aliasing
indented HERE
linearizable reads
Unicode collation
views
default to localhost-only
causal consistency
retryable single-doc writes
shards must be replica sets