I use Elastic Search everyday at work. It is a PITA. It scale poorly, it is super hard to configure properly, their environment is a mess, and even with the v5 they still have tons of problems of resiliency. (in particular, Aphyr broke it again...but he needed more time this time.)
And stability is really not that great. We have cluster dieing under us regularly.
And let not talk about the "facets" problem. So far, i would not advise to use ES before a couple other years to clean the problems.
It is not a bad search engine, but it is not a great document DB.