I think that reflects the complexity of a storage product more than CoreOS itself. I use CoreOS. I like it. I love the update mechanism, and the tight focus on running as much as possible in containers.

But I also have spent enough time using it to run across certain warts, and Etcd clusters refusing to start without manual intervention etc. have been a frequent enough problem that when they go after something incredibly hard such as distributed storage, and it's relying on Etcd, I see that as a scary combination.

Disclaimer: I work on etcd at CoreOS.

CockroachDB is built on top of etcd/raft package, not etcd itself.