Craftbeer.com has a great write-up explaining the history of Oktoberfest styles and medal-winners in each of the categories. Simply put, American Oktoberfest styles do not really match up with what’s going on in Germany:
Germany’s current version more closely resembles a dortmunder, a lager with a lighter malt character and color than what many in America would accept as an Oktoberfest. This variation is seen in the U.S. craft beer scene, specifically at the Great American Beer Festival (GABF) and World Beer Cup where the competition categories are “Dortmunder or German-Style Oktoberfest” and “Dortmunder/Export or German-Style Oktoberfest” respectively.
Märzen is not my favorite style, personally. This time of the year I’m much more inclined to reach for something further in one direction or the other–like a slightly lighter Dortmunder/Dunkel or something with a little more heft like a Doppelbock. So if you, like me, have sampled one too many Märzen over the years and figured Oktoberfest just wasn’t for you–well, you can try something else and school your friends that ought to know better.