Gummy has a gorgeous voice, if I may say so. It's smooth but it's got punch/kick/whatever. I wouldn't say it has a nice deep timbre, but it is a bit deep. She has technique, and she sounds like a seasoned pro on the song.
So the song. The song, the song, the song. I'm ALL OVER it. Like, ALL OVER.
It's epic, it's grand, it's gorgeous. The verses sound very Evanescence and then the chorus just explodes into this gargantuan, THING. The drums just make the entire song epic. Like, without that part this sound would probably be boring. The second verse also has this loop running around, it sounds as if it belongs more in an Usher or Chris Brown staple but you hear it and it's like it just fits perfectly.
Her vocals just compliment the song and the arrangement leaves you stunned - it's got intensity but it's also got dynamics. Like, she isn't screaming throughout the entire song, nor is she mumbling random sounds. Synths, creepy effects, strings and a voice like Gummy's - all the makings of a good "long-haired girl in black running through an old deserted house" song.
You strip away all these lavish instruments though, leave just a simple piano part following the vocals for time and/or pitch and you have a gorgeous song. Like, gorgeous - the melody of this just makes me melt, it's epic on its own.
Each part of this song can stand alone - the instrumental, the melody - but put them together and everything just explodes.