I thought Rammstein wasn't considered "proper" metal by most people around here in first place, but I was judging by a thread I found a while ago, so I might be wrong :-/.
Lyric-wise, Rammstein are just unreal. I know that it's hard to appreciate unless one speaks German, but the selection of words, the way the lyrics build up, the double entendres, just magnificent. The singer's books are great as well. Combined with the stage show and the authenticity (hell, who makes a hole in their cheek just to lead a cable through it to power a small light bulb in their mouth for a visual effect in a music video?), it's one of the few things where I feel like I get a complete "experience" instead of just a bunch of guys playing music.