I really liked RethinkDB (maybe even loved?), but its demise is one of those cautionary tales that makes me wary of these single-corporate-sponsor databases.
I’ll admit I definitely fell all the way into “loving” RethinkDB. I still have some sticker bundles from a meetup group merch package. It’s been an agonisingly slow recovery from the company’s demise, but I still hold onto some hope that it can recover and become a multi-stakeholder database with a steady development like PostgreSQL for the horizontal scale document database world.