We are using Zendesk for lots of things:
1) Ticketing system for customers concerns
2) Tracking of our progress for each project
3) Social media integrated
I say that I like Zendesk as a whole as we are using it for different purposes.
As for the features, Zendesk can be integrated to other platforms such as slack which is awesome. Another thing is that Zendesk is available in mobile application (but needs tons of improvement) which gives us the ability to track tickets on the go.
Zendesk also offers help center, wherein we can redirect our customers to answer any common issues. Not only customers would benefit here but also us, as we can create our own knowledge base, wherein it is not available for public.