It is imperative you must know about this sooner or later. If you are into e-zine publishing right now, this set of criteria will significantly enable you to tweak your layout and presentation to suit your subscribers' taste in general. It's brief but better than nothing.

Newsletter readers like:

Easy-to-skim designs
Short articles
Interesting subjects
Good visuals
Calendars
Bulleted Lists
Content telling how to make money/save time
Offers and Benefits

Newsletter readers DON'T like:

Intimidating pages
Disorganized information
Long, continuing articles
Overly frequent mailings
Irrelevant content
Impersonal tone
Receiving multiple copies
Chaotic page design
Too many pages