The current ESC key behavior is confusing and inconsistent:

• Hitting ESC while a popup is open appears to do nothing until the popup closes.  Then the Options menu pops up, which is confusing.
• Exception: In some cases, ESC immediately closes the popup and opens the Options menu, which is inconsistent.  Ex: the "Kingdom Report" popup.

The following would be more intuitive:

• If any "popup" is open, then ESC closes it (but doesn't open Options. Where "popup" is:
    * Any Menu (e.g. Options menu, City build menu, Kingdom report, NPC details)
    * Any Dialogue box (e.g. enter name of city to build, recruit NPC)
    * Any Book (e.g. book that covers screen at start of game).
    * Anything that pops up on the screen that isn't the main map.

• If no "popup" is open, then ESC opens the Options menu.

In general, this falls under the category of streamlining the interface.  There is a lot of "move mouse, then click X/Done/Back to Game", when all of these fall under the traditional function of ESC.