Hard to put into words except for "it just works". But let me try:

- The CLI / toolbelt is pretty amazing. You can do all sorts of analysis right in your terminal.

- The upgrading/crossgrading is pretty easy to.

- Attaching multiple, different apps is really nicely done.

- Extra, third party, services can tap into the logs and give you full insight into what the hell is going on.

The experience is really good, because there is no "experience". It gets out of your way and feels really robust and reliable.

Indeed; don't forget the follower databases (read replicas that can be upgraded to master).

RDS has read replicas and a process to promote to master that's just as easy as Heroku.