Festbier v. Märzen

I have sampled several Oktoberfest beers recently and think that I have figured out the difference between Festbier and Märzen. Festbier ressembles an Imperial Helles. Märzen ressembles a hoppy Scotish Ale with a clean lager finish and a malty flavor that accentuates toast or biscuit rather than barley or peat. Festbier is lighter, more quaffable, and simpler. Weihenstephaner Festbier is a great example of Festbier and Great Lakes Oktoberfest is a great example of Märzen. What BeerAdvocate says about the two styles follows below.

BeerAdvocate
Festbier is the modern day "Oktoberfestbier" that's served at the official Oktoberfest in Germany, as governed by the Munich city committee. Traditionally, the majority of the beer served was the dark, rich Märzen lagers that we've all come to love and associate with Oktoberfest, but that hasn't been the case since the 1990s. Now, it's all about Festbier, which is a bright and golden beer that's akin to an export-style (slightly stronger and maltier) Helles lager. Paulaner Brauerei is credited with creating the style back in the mid-1970s. According to many sources, their brewmaster wanted to give the people something "more poundable." Gotta love that.

Drinkers can expect Festbiers to showcase a clean, but strong malty backbone, light hop profile, and incredible drinkability.

And you might see the style referred to as Wiesnbier, Wies'n, or Wiesn. The latter is what locals in Munich call Oktoberfest, based on Theresienwiese, which is the meadow/fairgrounds where it's hosted. This is not to be confused with Weissbier, Weißbier, or Weizenbier (wheat beer).

BeerAdvocate

Märzenbier ranges from dark amber to deep copper in color. It's a full-bodied lager that's rich, malty (toasty, bready, biscuity, caramel, roasty), moderately hopped (floral, spicy, herbal), and finishes clean and dry like a good lager should. Alcohol can bite and warm a bit, but overall should be tame.

Historically, Märzen (March in German) was brewed in the spring, lagered in caves (stored cold) during the summer months, and served in the fall. From 1872 to the 1990s, the style was served at, and widely associated with, Oktoberfest in Munich until the lighter Festbier became popular and adopted as the official Oktoberfestbier. That said, brewers around the world still brew "Oktoberfest" and "Fest" beers that lean toward the Märzen style.