I saw Apocalyptica earlier this year, and I went because I wanted to hear the classical style, but with a metal twist on it. Sure, it's not metal at all.... But it's got that classical style, with a harder edge to it. It's an acquired taste, honestly. Not everyone will like it, but those who do, really love it. But if you went to an Apocalyptica show, expecting to hear metal.... You obviously haven't listened to them much, and that's just... kinda your fault. Not really anything wrong with that, you just went to a show thinking they were one style of music, but they were another.
Apocalyptica is way more than a Metallica cover band now. People don't go to their shows for the Metallica covers. Their fans are more into their original pieces, and the general sound they have. The covers they do now are mostly for their own fun, since that's how they started off.