Too many emails!
While notifications are important, I don't know if it's necessary to send an email update every time someone makes a move or leaves a comment.
Would it be possible to opt-out of specific kinds of notification, or have a daily/weekly/etc digest option for each game?

Storium now gives you several options for managing your email notifications. You can receive all notifications, or you can receive a single email digest per day, or you can receive a daily digest plus anything important or time-sensitive. This can all be managed from your Profile page. There is also a link in the footer of any email you receive from Storium. Note that even when you have selected to receive all notifications, comments are automatically digested so you won’t get an email for every comment.