An heuristic evaluation, as originally outlined by Jakob Nielsen (in collaboration with Rolf Molich), is a rapid, lightweight, and inexpensive process for ferreting out and prioritizing usability issues in an application, web site, or any other virtual or physical interactive medium.
For this project, I recommended and conducted the evaluation (more precisely, I took a hybrid approach, incorporating many facets of a cognitive walkthrough) based on the developer's tight time frame and limited programming resources. The goal was to find, within a week, the top trouble spots to address for the next revision of the iOS app.
This approach requires the "expert" conducting it to stick strongly to the user's point of view and not allow experience with the app in question or with design principles interfere; I call this a kind of radical empathy, and am well practiced in it.
Within a week, I had cataloged the major issues that were in conflict with Nielsen's heuristic principles and categorized them by type and severity. This allowed me to rapidly sketch and prototype interactions that would give the user better understanding of the app, more control over his or her data, an improved and less frustrating interaction flow, and more confidence and less stress when using the app.