I did some testing with the interface that looks a lot like the Apple Mail Rules dialog, and received the following feedback from users:
Way too many click actions
Unclear what a rule does
The above feedback seem to mostly apply to long rules with a lot of added options or just a lot of rules in general. User with a few short and simple rules didn't seem to have a problem with the interface.
What would be a good way to reduce the complexity of the dialog if the user adds a lot of comboboxes