Perhaps the most complicated application I have ever worked on, Arena by Altitude Digital, is so complex that it is constantly evolving and improving. Arena is a powerful Supply Side Platform, (think automated media purchasing) and it needed simplification. I was involved in an early iteration that addressed the most basic needs.
First we tackled the reporting page that they claimed was so bad, they refused to show us what it looked like. All we had to work off was an outline they provided.
We took on the Publisher page next, which was quite convoluted. We were able to simplify it with a series of expandable rows and dropdown menus.
Due to time pressures, we weren’t able to overhaul the entire UX so the ideal UX experience was reserved for phase 2. By segmenting the most popular parameters we were able to reduce the controls to more manageable sizes.