I've recently declared emacs bankruptcy and in rebuilding my config switched from the old python-mode.el to the built-in python.el. 
One thing that's I'm missing is the old behaviour of auto-indenting to the correct level when hitting RET. Is there any way to re-enable this?
In upcoming Emacs 24.4 auto-indendation is enabled by default thanks to electric-indent-mode.  Since Emacs 24.4 has been in feature-freeze for quite some time now, there should be no major breaking bugs left, so you could already make a switch.
Enable auto-indent in python-mode (python.el) in Emacs 24?