Synthetic Oil - good or bad?

i've been running synthetic on all my cars and trucks for 30 years never had a failure and i drive my cars until they hit 350,000 miles . even my 340that i tore down at 10,00 mile looked brand new inside no wear on any bearing . none of my car even burnt oil between changes usually 5000 to 8000 miles might depend on the synthetic oil you buy , so far royal purple valvoline and total have been good to me