Heavenly (metal version) is so called "power metal" which is very different to the stereotyped view of metal.
To describe power metal I'd say there's two types.
First the type of power metal in which they mostly sing about fantasy themes and "epic stuff" while using heavy harmonising + choirs (note that coarse vocals or "deathgrunts" are not used), or in my terms a bit mono toned in length.
Then there's this type of power metal which is more of a genre where the artists try to keep a rather high level of musical quality (in terms of composition) compared to most genres.
Because of that most of the headbangers (those who listens to the heavier and coarser styles of metal), and many others, tends to say that this genre is rather queer when it's more of a matter in what you're after when listening to music.
Personally I love this group (yet again, the metal version) because they have very interesting tunes and a specific sort of feel to their songs.