Now this is a database whose every release brings something genuinely useful. I am really glad this exists and gives me a good measuring stick to compare to other db's.
I hope that it ends up as a MongoDB killer within the next few years. They certainly deserve success.
Explicit control over write durability and out-dated reads alone is a pretty big advantage. When you start to factor in how much better ReQL is and the atomic nature of ReQL queries RethinkDB pulls far ahead.
I didn't try some big instalation, and I would expect at least some issues, but generally, so far, sun is shining each time I use RethinkDB