I personally did a little "festival tour" for the last two years. I go to Finland to see all the great festivals, then head over to Northern Germany for Wacken, then back to Finland. Works great for me.
Forget about finding a hotel if you're not booking very very early. And if you can, rent a car to sleep in. The weather can be very nasty (torrid rains and heavy winds) and in such a case, it's better to be inside some vehicle.
As Wacken is such a big festival there's always a lot you could complain about, I just say "bear it and grin". Most of the festival goers do that. The atmosphere is friendly and there's so many bands playing that there's something for everybody. Just print out the running order and mark all the bands you wanna see.
I like that.