I've always just called them Progressive Rock. Progressive as a genre often includes many other elements of different genres anyway. However, it's kind of hard to ignore how similar the vocals are to that of an Emo singer, so you could call it Progressive Emo. There's no denying the emo and post-hardcore influences, so yeah, progressive emo is suitable. I've always loved how they can take a relatively simple time signature (say, the 6/8 of In Keeping Secrets of Silent Earth: 3) and syncopate it so it sounds like something totally different. It makes the music really interesting. And @ Dragoonson: both eras of Nightwish are symphonic power metal.