Agreed! I had tons of fun building my own CMS on top of RethinkDB (as well as a logging/journal app for personal use). The only reason I ended up with a wordpress/MySQL solution for the CMS was that building the CMS interface is a bitch and migrating from SQL to SQL was a bit easier.
It's an awesome database for a variety of use-cases.
Personally, I think their query language + support for joins makes it much more useable than MongoDB (which I've used quite a bit).