$3 million would put me into comfortable retirement.
$300-500k for a good waterfront house in my province, $2mil invested for living off interest long term, remaining amount to put into lifestyle and projects over the period of several years.
Remember though with inflation, living costs, taxes etc $3m in 20-30 years time will be like having 500k-1m today.
Also you have to account for rising health costs when you get older one day you wil have to pay for a caretaker also. These are hidden costs that you have to account for later in life.
I personally think of a figuire I can live on very comfortably today and then triple that.