It goes on forever, it's pointless, it's repetitive, it just sucks and it sucks for a very long time.
But there are a couple good spoofs of it, one by Bob and Doug McKenzie (”and a beer/In a tree”) and one by Bob Rivers
(”hangovahs/ riggin’ up the lights/ And finding a Christmas
tree”). Oh yes, and Allan Sherman too while I think of it
(”and a Japanese transistor radio”)
Oh I love the Muppet version with Miss Piggy singing the 5 golden rings part.
John Denver was on their Christmas show and sang with them.
http://www.bing.com/videos/watch/video/12-days-of-christmas-muppets-and-john-denver/d49014d8089800110afad49014d8089800110afa-280733614231?q=muppets%2012%20days%20of%20chirstmas&FORM=VIRE3