Hello Rosalie [Reacts] !  Nightwish fan here, your musical quest summoned me.
Welcome to the world of symphonic metal! And thank you for checking this legendary band! Many thanks to Brandon for introducing you to this band :) This song was performed in Wacken Open Air in 2013, together with Floor Jansen [pronounced Yansen], the 3rd and present female singer of the band, in front of an 82K audience.

About the instrumental and vocal added parts - it's good to know they recorded their orchestral and vocal back tracks with prestigious institutions as London Philharmonic Orchestra. London's The Metro Voices choir group and London's Young Musicians Children's Choir as their regular partners.

Since this is your first Nightwish reaction, it is my duty to give you the [updated] short history of the band concentrated by Ann Waychoff, one of the biggest Nightwish fan who has since passed away (and I am doing this in her memory):

" Nightwish was started in 1996.They are considered a Symphonic Metal band, with a female main singer. They are from Finland...

Tuomas Holopainen is the keyboardist and he's the main man behind the band who writes the vast majority of the music. He also writes the orchestral parts. The guitarist is Emppu and he's the character in the band, though they all have their moments. At the same concert during "I Want My tears Back" Emppu messes with Floor's in-ears and it's a real laugh when you know what is happening. In other concerts, Floor has chased Emppu across the stage. When Floor goes dancing, Emppu gets the hell out of the way as the poor little dude would get run over. There's loads of these little moments scattered throughout their songs.

Watching people react to this is one of my guilty pleasures

Someone described this band as A Pirate on Drums, a Viking on Bass, an Elf on Guitar, a Dark Wizard on keyboard, and a Valkyrie on Vocals!

Floor was on top of her game for the whole concert and the band recognized that right away.  Floor had not been with the group that long, so they were still getting used to each other.  That night helped.

Whoever mic'd those drums deserves a Grammy.

I love when reactors are blown away by Floor the second she opens her mouth and we all know ........wait , just wait , you haven't heard anything yet.

Evanescense, Amy Lee? Come on folks!  This is Floor Jansen,  6Ft Valkyrie Goddess of Metal ......

Best part?  Imagining how many young girls are now inspired to be in bands.

Tuomas is not the guitarist, he is on the keys and he is the mastermind behind their music.

Those goosebumps you felt when she started singing are what's known as a "Floorgasm".

The symphonic part is actually the London Philharmonic Orchestra with their choir.  Nightwish uses several English choirs to add to their music.  Floor is technical a lyrical soprano but has the range to sing some alto notes.   She also growls and can hit a very clear D6.   She's got it all.  BTW, there is a video of her actually singing the phone book.   Someone bet her she couldn't do it but she did.

First Floorgasm of the day. Floor is 50% Dutch, 50% Elf Warrior Queen, 50% Nordic Goddess - 150% and upwards.

WAIT FOR IT.......... THE NOTE THAT LAUNCHED A THOUSAND SHIPS ❤🎙🎶🎵🎼

As an old time rocker starting in the 70s , I have witnessed an untold number of live performances in my lifetime. This is in my opinion one of the greatest live performances , not only in rock, but any genre ,that there  has ever been. Totally flawless , and to think they can pull this off live is amazing.

Originally Floor was sent by Allfather Odhinn to Midgard to gather the souls of fallen warriors to Valhalla, but she
got distracted and joined a series of bands. However, Floor still gathers souls by her grace, beauty and the sheer power
of her vocals.
We give thanks for her at our Blots regularly and hope that Odhinn won't notice that she has never returned to Asgard.
ALL HAIL THE VALKYRIE GODDESS!!!
The Nightwish Army is incoming! You're not ready!
Nightwish Army Central Florida Black Company reporting for duty!

Floor is the only woman yet who never fails to brings me to tears with her voice. I dont know how, or why but she just does. She is just magical.

She held that last note for 8 seconds. But if you watch the more recent concerts, you will find one where she did it for a whopping 15 seconds! Small correction to what Brandon said: Floor studied rock and had a year of opera training.
Floor can do whatever she wants to with her voice. Her abilities go from opera style to growling like a lion.

She only got 48hrs notice to do her first show with Nightwish to learn the entire set and she nailed it from the first show.

I can hear them, the footsteps of the army are echoing... The Nightwish army is coming!!!!