I listened to the whole song. It is very bad. Corden's shouty vocals are mixed too high; they sound awful.
In the second verse, they start doing little comedy interjections between each others' lines.
They should play this song to everyone in the country one at a time, and if anyone likes it they should be drowned in a toilet, and then this would be the best country in the world.
Last few lines:
CORDEN: I was the best in that song
BARLOW: So was I
BARLOW (spoken): It's my album you know
Painful. I don't think I've ever heard a more nailed on Christmas number one.