The Windows 8 Store is improving their feedback when errors are encountered. The now provided notes of the error encountered and a PDF with even more information.
I have been hoping the store would start providing this information. The Windows Phone Marketplace has been providing this level of feedback for some time now.
A caveat, the submitter still must interpret what is said in the notes. The notes read like something on the dead sea scrolls.
Notes from Testers:
B:: The website(s) submitted with the app do not appear to be completed. A:: This app failed performance test in the Windows App Certification Kit. The Performance Analyzer for HTML5 Apps enables you to find common performance issues in your app that prevent it from being fast and fluid. The tool tests your apps in a wide variety of scenarios including fast UI responsiveness, fluid graphics animations, activation time, suspend times, memory foot print, memory leaks, Idle efficiency, and touch responsiveness. See: http://msdn.microsoft.com/en-us/library/windows/apps/jj553524.aspx
Here is a screen shot of the PDF. They even highlight the pertinent areas.