I'm glad that it isn't Wacken. You have to know that in meantime Wacken's reputation isn't the best one in Germany, because in the last 10 years it evolved to a big sellout-metal-funfair where only cash is the intention for doing this festival.
In opposition to that the Party.San Open Air owns still the underground-intention where fans organize a festival for fans. This festival has also big dimensions and has enormously grown in the last 10 years, but it has still the underground-attitude (just look at the fair price of 39 Euro and all the Undergroundbands) which I and many other Germans prefer.
Just read the news for the Wacken-Poll and all the discussions on the Bolt Thrower-Page and maybe you will understand what I mean (
http://www.boltthrower.com/news/news.php).
Im very, very happy to see Bloodbath on such a festival