How about being able to talk to your customers on a personal level and professional at the same time but all at the same time.
How about being able to see which customer clicked on which link, so you can see their interest?
How about being able to see where in the world the email was opened up from as well?
Knowing that your emails are mobile friendly as well as tablet and desktop.
Being able to automate your emails to follow up.
Being able to see live as it happens the results from your email as it goes out.