With the proliferation of apps and a new generation of web services, the bar for software usability has been raised. If your software isn’t simple enough to use, it will be replaced and obsolete in a few short years.
Some used to believe that the complexity of the task being done (accounting, 3D Modeling, statistics, etc.) forced the software to be complex. That was before products like Mint, iMovie, and Mailchimp proved them wrong.
How simple is good enough? If it requires to user to read documentation, it isn’t good enough.