We've had the same experience. It adds just enough convention on top of Backbone to prevent your application from turning into a ball of mud, while at the same time remaining small enough where you can hold the whole framework (Backbone + Marionette) in your head. I find Backbone + Marionette much simpler, and much easier to reason about than Angular, but keeping it this way still requires developer discipline. Avoid hacks, avoid event soup (which Marionette maybe makes a bit too easy), and follow general object oriented design patterns, and it's not that hard to build a maintainable, scalable Backbone/Marionette app.