>Optimize for programmer happiness
I've never been more unhappy programming than when I touch Rails. I'll take python or Java any day of the week.
>Convention over Configuration
Discoverability is totally gone. Walking into a brand new RoR app and it's next to impossible to figure out what's going on. Not having a good IDE doesn't help.
>Exalt beautiful code
Write simple easy to read code. Don't be clever.