As mysterious as they look, stouts are typically dark brown to pitch black in color. A common profile amongst Stouts, but not in all cases, is the use of roasted barley (unmalted barley that is kilned to the point of being charred) which lends a dry character to the beer as well as a huge roasted flavor that can range from burnt to coffee to chocolate. A different balance of hops is up to the brewers preference, but the roasted character must be there.
American brewers have taken this style to a new level. Whether it is highly hopping the brew or adding coffee or chocolate to complement the roasted flavors associated with this style. Some are barrel aged in whiskey barrels. The hop bitterness range is quite wide but most are balanced. Many are just easy drinking session stouts as well.
Russian Imperial Stouts (RIS) are inspired by brews back in the 1800’s to win over the Russian Czar, this is the king of stouts, boasting high alcohol by volumes and plenty of malt character. Low to moderate levels of carbonation with huge roasted, chocolate and burnt malt flavours. Often dry. Suggestions of dark fruit and flavors of higher alcohols are quite evident. Hop character can vary from none, to balanced to aggressive.
Oatmeal stouts are generally medium to full bodied with an unreal smoothness from the addition of oats to the mash. The oats also give a touch of sweetness that is unlike any other type of stout. Both levels of roasted flavor and hop character will vary.
Milk / Sweet Stouts are basically stouts that have a larger amount of residual dextrins and unfermented sugars that give the brew more body and a sweetness that counters the roasted character. Milk Stouts are very similar to Sweet Stouts, but brewers add unfermentable sugars, usually lactose, to the brew kettle to add body and some sweetness. (BeerAdvocate)