Recently , I was participating in the Project Server Upgrade from 2010 to 2013. The migration process was typical and well described in Upgrade to Project Server 2013
After migration was over, I have faced several issues in Project Server 2013, which were confirmed as bugs by Microsoft and as of October 2013 most of them were not resolved.
Project Server 2013: Can't close the period - already resolved
Project Server 2013: Timesheet.aspx. The view failed to load.
Project Server 2013: TS Approval history wont' show filtered by Resource name