Kreator is pretty much the biggest German thrash band, and for a good reason too. They're awesome. Even nowadays, their music is just as heavy as it was in the 80's. And the production's better too. But the album that established Kreator as one of the head-honchos of thrash was 1986's Pleasure to Kill.
This album, for lack of a better word, rules. These guys know how to thrash. The riffs are fast, the lyrics are brutal; it's like Germany's answer to Reign in Blood.
The only bad thing is, it's not as good as Reign in Blood. The only problem with Pleasure to Kill is its vocals. And that's only when their drummer is singing. He's basically Governor Arnie singing thrash metal. But when their guitarist is singing, it's simply thrash perfection.
If you like thrash in the slightest, acquire Pleasure to Kill right now. It's pretty brutal. And awesome. If you can get past the bad production (it's like Kill 'Em All) and the drummer's Hitler-esque vocals on some of the songs, you'll love this album. If you like thrash, that is.