As a computer repair technician for over 20 years, I've handled no shortage of data recovery cases. Most were just logical cases where the file table was corrupt, or the drive had been formatted / overinstalled with Windows, etc. It's usually just a matter of running your favorite data recovery software like Recuva, R-Studio, GetDataBack, or another and sorting through what it finds. Occasionally I ran into the tough cases where we had to try and image around the bad sectors using a tool like dd or ddrescue.
However this week for the first time I found myself in totally over my head. The issue was logical in nature I suppose. Was a perfectly healthy RAID array last week that suddenly had a motherboard failure. After replacing the motherboard, the controller would no longer recognize the RAID array and allow it to be used. It just prompted to create a new array.