The ability to see, and drill down to, all of the metrics that are available for any given campaign. I wish that there were more metrics available. The ability to use the API to build custom dashboards is a huge plus for me. I can easily create custom dashboards that show metrics not available through the main dashboard. I also like that all of my email campaigns are stored in one place, which makes managing them much easier. I dislike that the dashboard can be overwhelming for a first time user. The ability to create custom dashboards for any given campaign is a big advantage. I can customize the dashboard to best suit my needs.