A research team in Europe used science to explain what made Freddie Mercury's voice so great.
The key lies in Mercury's vibrato, which differs slightly from those of other classically trained singers. Typically, an opera singer's vibrato has a frequency of about 5.5-6 Hz. Freddie Mercury's is faster, and it's also more irregular, and that creates a very typical vocal fingerprint. Now you know.
Thanks to New Deal Progressives for passing this along to me.