The best about Ember is Convention over Configuration in its tool - Ember CLI. The organisation and structure of complex projects is great. Also, the components, the bindings, Ember Data, routing, everything together gives great experience of creating complex SPA applications. Ember Data makes it straightforward to work with your API backend and manage models.
Compared to for example Angular I'm happy that Ember comes with Ember CLI. You have best way how to do things shown in the Ember Guides. You don't have to find how to organise project in some tutorial or article like its in Angular, but you can actually jump right to developing applications by running simple command ember new my-new-application.
What I dislike about Ember is its performance compared to other frameworks. Also, sometimes Ember CLI was really painful to work with (you spend hours on struggling with Ember CLI tool instead of developing you application and writing business logic).
I'm creating applications in business area like working with claims, insurances. Ember makes it easy to work with backend APIs. Also it's easy to create custom UI widgets and complex logic. For example, you might want to create multiple select elements synchronized with each other (element is hidden from the global list if it's chosen in one of the select elements). Ember lets you do that.