Etcd (at least up to 2.1, which I'm running now in prod) doesn't bother with niceties like service discovery and failure detection; it's strictly focused on serving as a distributed k/v store. I think that's the biggest difference I can think of.

I'd disagree with the stable/reliable bit; or, at least, I'd note that CoreOS ships with etcd, and fleet (the CoreOS job manager, at least until Kubernetes obviates the need for it...) depends on etcd to function correctly.

The upshot of that is, if you're running a stable release of CoreOS, you have a stable etcd, by definition - or you have a broken cluster that you can't submit jobs to, which would be bad.

From the outside looking in, to me Consul seems to provide more features; I don't doubt that it's awesome, but etcd ships with CoreOS, and when I spin up a new cluster via Cloudformation it's up and waiting for me as soon as I log in. This is a huge selling point, as I am lazy.