Slayer were good at Donington Download 2004 too. They were the only reason I went really (just for the Sunday), as I am not exactly a fan of Slipknot, and although Metallica were there, they were very late and played a lot of new stuff.
Slayer actually gave up their main stage spot for someone else that day, becuase someone was running late. They ended up on the second biggest stage, which was in a huge Marquees tent. It worked out much better this way, as it was dark in the tent, with red stage lighting, and it was a boiling hot august. It gave the tent great atmosphere. They played basically all of Reign in Blood and a few others. Great gig.