I think it's very mature power metal; not the formulaic traditional stuff. Granted, their older material is a bit formulaic (The Black Halo is a recent record), but it still retains a certain originality. I think they're one of the more creative and innovative power metal bands. The Black Halo definitely showcases some of that creativity.
But I'd recommend you pull out Epica again, and if you find yourself enjoying it, check out The Fourth Legacy and Karma.