Having worked with the Interactor gem for a little while once you break things down into small interactors that can be used by the Organizers, I have two main complaints.
1) inputs are unclear. With calling new or some custom class method you can use descriptive variable names to say what the object expects to be present to do it's job. With the Interactor gem you end up adding in comments describing what keys need be present in the context and what keys will be added to the context so the next programmer can use the interactor you've created without having to go through and grok everything.
2) You end up having to (re)create a failure protocol to communicate with the controller and display to the user. We take the AR errors functionality for granted in our controllers/views with interactors you have to come up with a similar system.
2.5) as a result you end up writing a lot of boilerplate fail! and rollback code
2.5.2) and a non-atomic operation like notifying the payment gateway can break the whole model of rolling back and you have to end up raising so your user doesn't end up in a invalid state or get charged twice.
We've got a convention that all Interactors must be commented to specify what inputs they take.