The UI for Flow is generally pretty good. However, when multiple decision trees are used, the layout can get pretty convoluted and hard-to-follow (see one of my Flows below):

In these cases, even the auto-arrange fails to make this something that a normal person can easily look at and diagnose.

One thing that might help is to have the ability to collapse (and un-collapse) downstream actions within the UI. This would help to better organize and troubleshoot.