In[4]:= % // UnitConvert
Out[4]= Quantity[6.674*10^-11, ("Kilograms" "Meters")/("Seconds")^2]
In[5]:= % // UnitSimplify
Out[5]= Quantity[6.674*10^-11, "Newtons"]
Thank you. i didn't even check UnitConvert because it's not a conversion (not what Convert[] did in 4.0 either). UnitSimplify[] was not in the See Also of help for Quantity[]. The overview didn't mention UnitSimplify (but I did miss finding the Unit guide page).
I really don't like the "1st generation" oob style solution, but at least it can be made to work.