Agree. Some cover versions improve on the original, but sometimes the original song is so good or distinctive that almost any cover version is going to be not worth the effort.
Good cover versions:
Melanie - Ruby Tuesday
Hendrix - All Along the Watchtower
Santana - Black Magic Woman
P.P. Arnold - The First Cut Is the Deepest
Bad:
Judas Priest - Green Manalishi
Céline Dion - River Deep, Mountain High
Absolutely, unbelievably and ineffably atrocious:
Lulu - The Man Who Sold the World