I like how easy it was for me to set up my data validation rules, as well as using their API integration which makes managing multiple lists much easier! There are some minor glitches in terms of being able to send out emails through other systems (ex Google Apps), but this has been remedied recently so not too big deal there either - just make sure you test everything before sending anything live!! The ease at integrating different mailing services into one platform really helped our marketing team streamline processes across all accounts we manage within MailChimp/AWeber etc.