1. Gregorian chant--rocking the world since AD 598.
2. Rich yuppie + conversion experience = monk.
3. non angli, sed angeli. And the heathen English all rejoice.
4. The Super-duper Roman bestseller, Pastoral Care
5. Lazy clerics + Papa Gregory = Sudden feverish activity.
As against that, John Calvin actually liked him, calling him "the last good Pope."
Luckily, back when the Curia didn't take ages to do anything, they canonised him anyway.