Yes. I have switched back and forth between them before. The main advantage of Cassandra for me is that it is multi master. This makes it perfect for the cloud where you can trivially scale horizontally whether in the same AZ, across multiple or even across entire DCs with just a config change. It really is a dream to deploy and manage.

MongoDB is a document store and so if you data is structured that way it is unrivalled. But if isn't (more than likely) than it will suffer greatly as you start to increase the number of joins.