I like that it's easy to set up, you can even use your own email address for receiving emails from other people if they have an account with any of the major providers (Gmail, Yahoo etc).
The interface could be improved - some options are not obvious at first glance or require too much clicking around before finding what you're looking for. It does everything we need without being overly complicated so far. We've been able to move our business communications into one place instead of having multiple accounts across different platforms.