If a beer has been brewed well (sanitarily, proper pitch rate, proper amount of oxygen) then when it is green it should mostly taste a little yeasty, spicy, maybe sharp, and not very complex. Or should I say, you can't taste the complexity because other strong harsh flavors are present.
Fusel alcohol should be a very sharp burn in the nose and very "hot" tasting.
I reguarly keg my beers after 6-10 days once the diacetyl test is negative. While they always taste better after another week of aging, I like to taste the evolution of the beer... so what I'm saying is I'm pretty familiar with what green beer tastes like (with the London ESB strain).