There is a hidden 8-bit retro mode in Broken Age that resembles early PC adventure games. Here's how to unlock it.

In the options menu, set the resolution to 640x480.
Activate "key remapping"
Look for a new button showing Shay and Vella in the lower right and click it
You can now use this button during gameplay to toggle between resolutions.

You can also map a key for the Shay/Vella button, allowing you to toggle between resolutions quickly. When you do this, you can actually change the game's resolution back to your your monitor's resolution and still toggle between a retro and modern look. It looks much better this way, since it's not stretched out.