Melody and a graceful delivery is the key word for Sonata (example; the ballad 'Under Your Tree'), not really heavy or aggressive for metal, well maybe at times, but the vocal lines by Tony Kakko are always up in front with backing vocals a focus for the songs. 'For The Sake of Revenge', 'The Vice' and 'The Harvest' while use edgier guitars and a harder delivery still carry a melody first and foremost. For the most part Sonata Arctica’s keyboard use does take president over the guitar and serves as the music’s driving creative force.
Let's see where they take the music next time I’m curious.