I would give this 5 tacos except it is not as powerful as some Project Managers I have found on AppSumo. However, Dart is easy to grasp and use right away. Two things I love about what Dart offers:
1.) A really nice Gantt chart view Dart Calls "Roadmap"
2.) Unlimited parent/child/grandchild/etc. task structure which means if a project has a task in it which becomes a project in and of itself (happens a lot working with agencies), you have unlimited hierarchy to represent however complicated it becomes. This isn't particularly "Agile" but when the world get's complicated and out of control, this feature helps reign it in and show stakeholders that the scope has exceeded expectations.