I attended in 2002. Basically each tent serves its one beer - as to the style - its a slightly more hardier version than each breweries helles (almost maibock like) - some bolder than others malt and hopwise. I believe a couple of tents offer hefeweizen - weinzvelt? Hofbrau and Lowenbrau are some of the lighter versions - and hacker pschorr being a bit more amber colored with enough hops to notice. Its meant to be drinkable since you are going to DRINK - a liter (~3 12oz. beers) at a time - drinking more than a liter or two of sweeter,thicker, richer marzen style would be difficult to do. Its probably not something a US beer geek that's used to a wide variety of selections when they drink would enjoy, but its more about enjoying the people, food, music, etc and having a good time drinking beer, than a focus on tasting beer.
I am also curious about the beers served at the Munich event. I have often heard that, as Mr. Dorsch says, the beers currently served are light colored lagers, rather than the amber beers that the Munich breweries export to the US as Oktoberfest beers. Has anyone who has attended recently shed light on this subject?
Since no one has replied, I will tell you what I know, even though I have never attended.
My understanding is that it's kind of a hassle, something you want to do once, but perhaps not again. The beer is all from breweries within the city limits. Most beer is the modern fest lager, a golden beer, sort of like an amped up helles. You can find traditional Maerzenbier if you know where to look.
I will let others with more experience comment on this and let us know if I'm off base anywhere.