We played Milwaukee last year. And as a fan it was still quite entertaining. Milwaukee is more of a death metal/harsh vocal style friendly festival, although many good melodic, power and thrash metal bands played.
It's indoors at the Milwuakee Auditorium. There is a main stage, and on that floor in the back is the vendor area with tons of music, shirts, for sale; plus many labels have their booths set up there. The main stage is in a medium size arena that maybe would hold 7 or 8000 people if packed. Then there are three smaller stages in adjoing rooms. Leaving the side of the large auditorium you enter into a big hallway. On either side are two smaller rooms, maybe the size of large cafeterias. Each has a stage and a respectable P.A. in it. Upstairs is the last stage in a theater-type room. The three smaller stages perhaps could hold 300-500 people each. Many of the more black and death metal bands, even the big names, play the smaller stages. Yet the biggest of the big play the main stage. Among last year's main stage performers were Soilwork, Anathema, Primal Fear, Amon Amarth, Jag Panzer, Steel Prophet and Helstar. On the side stages extreme metal bands like Krisiun, Zyklon, Darkane, Limbonic Art and Einherjer played.
The festival starts at about 2PM on Friday and goes until about 1AM. On Saturday it starts at about 11AM and goes until the same. There are probably more unsigned bands than signed ones. That's how the promoter pays for many of the signed acts to come. It costs a band $1000 to play the festival if you have no label. You receive tickets in return to sell. So in a way it's a win-win situation for the promoter. Whether the people actually come or not is immaterial, he's made his "ticket" money up front.
The sets for all but the biggest bands are only 25 minutes. Even Jag Panzer only had 25 minutes. But, with so many bands it strangely enough is about the right amount of time to see a band. The big headliners get from 45 minutes to an hour. I think last year there was 160 bands total over the two days. So you get to have a taste of everything.
I have never been to a large European festival, even as a fan so last year was much, much fun. The marketplace is very respectable, and it was just fun being a part of the crowds who were 100% metal. It's a big deal here in the US because metal is so underground. That is the largest gathering of real underground metalheads I've ever been amongst. Lots of fun! We very much look forward to playing again this year.