Listened.
Sounds like Once for the symphonic parts.
The voice is pretty... classical. Nothing special.
But there's no relation with Within Temptation, for me.
About the mastering, I wonder if it's not the quality of the file you got, more than the real quality.
For the music itself, it misses a bass, drums and guitars during the main part of the song.
(Anyway, excepted some pieces on Oceanborn, Nightwish isn't that great (imo), but I hope for some evolution. I can dream, I think)