What does Salesforce Email Studio do well? Building emails in Salesforce is not nearly as painful as other platforms. That said, no email builder is perfect, but there are a few features from other platforms that perform better than on Salesforce.
What does Salesforce Email Studio not do well? Unlike MailChimp, the Salesforce email building experience is less drag-and-drop and more manual labour.
What do you wish you had known about Salesforce Email Studio before using? If you're all-in on the Salesforce lifestyle, you don't have much of a choice but to use Email Studio for your campaigns. The integration with Salesforce CRM is at once its greatest and worst feature. Deep integration, but you're locked in.
Have you used a competitor to Salesforce Email Studio? If so, how does it compare? Since it integrates with the entire rest of the Salesforce stack, email studio is the best (and sort of only) way to build emails that can pull information from the CRM in an intelligent way.