RethinkDB looks really nice, was really easy to play around with it when I last did. I'm considering using it for a small project, but wondering what everyone thinks of the downsides, compared to the upsides. (there are pros and cons to everything :)).
Minor failover is automatic, but major failover requires manual intervention to repair tables even when there's no data loss. That's a little confusing and not obvious.
The anonymous function query style can get confusing because it is partially executed client side and then executed server side. This can be a subtle source of bugs.
Source: I am the creator and maintainer of the Elixir driver for RethinkDB.
Wasn't this fixed in RethinkDB 2.1? Or are you referring to something different?
Edit: it's better documented now, but still not obvious. https://rethinkdb.com/api/javascript/reconfigure/
I've never encountered it organically, but did during some benchmarks when I was dropping and adding a bunch of servers.