for a shooter -where the player need a constant good overview -
it should be 85 to 100,
I always put it to 90.

For an RPG maybe 80.

(FOV should be adjustable, its one of the most important
graphical options)

But One reason why I did not continue with MassEffect was the
ridicusly low FOV. Its very distracting not to be able to see
the scene propperly.