I like that they have such an easy process for creating my campaigns, it makes me feel more in control of what's going out into our email list than other platforms we've used before (like MailChimp).
Also their support team really listens when you're having issues or questions - which isn't always true with some companies/platforms!! They also offer several different pricing plans depending upon how many emails are sent per day / week etc., but if there were only one thing about this product i would change nothing because everything works great as advertised. We love using EMarketer since its so simple & intuitive once set up correctly for us!