Ok, I like metal, especially the powerful and melodic type. But this is ridiculous! For days and days different parts (not just one) of this song have been running through my head. On the bright side, I must confess I really love this song! In my humble opinion I consider it a masterpiece, and also many others think alike.
The song is "Light of Day, Day of Darkness", by Green Carnation. It's a 1 hour track (!!) and it's the only song of an album with the same name (no surprise there) released in 2001. Tchort (the band leader) composed this album/song largely inspired by the death of his daughter and the birth of his son. I think this is why you can hear a baby's voice and probably why some parts are so dark and sad, while others quite happier.
Even though this song is from 2001, I never came across it until two weeks ago. And despite the song's length, I can listen to it completely without getting tired or bored at all. It's like watching a move you love. I hope you can enjoy it as well.
If you don't want to listen it all through, I recommend you at least listen to these parts:
3:56 - 6:40
8:41 - 10:34
14:08 - 15:18
(There are many other excellent parts too).
More about this song:
And if you are curious about this "song stuck in my head" thing: