Both are crime solving dramas involving a great cast. however the main leads in Dr.Qin don't have any romance; its just friendship but the chemistry for friendship was there. I thoroughly enjoyed both although Dr.Qin is a bit more gruesome and involves more medical aspects
Both dramas shows the use of forensic pathology to solve crimes and catch the killer. While unnatural death solely focuses on the forensic part, Dr Qin includes police work too.
Both have excellent female leads but Dr Qin is more graphical.
Although both the dramas are set in different time period, they are similar somehow in relation to the investigation and follow-up examination. My roommate is a detective has elements of romance while the Medical Examiner Dr.Qin has very little or almost no romance (from what I recall).