Every cover they do is an improvement on the original.. have you heard the original version of Helpless??.... it's terrible
Metallica didn't make songs by Mercyful Fate, Motörhead and Black Sabbath better than the originals. There are others too. I don't know all of the covers that they've done, but they aren't a magic band that makes legendary music better.
Speaking of Metallica , Cannibal Corpse did a pretty good cover of seek and destroy...... as for Metallica covering Motorhead or black Sabbath, it would be kind of like ketchup and ice cream. They are both good for separate applications but not together
Too bad that the prevalence of Filosofem using the German label's song titles rather than the actual ones carried over to even that awesome cover.
Another vote for Metallica doing some fucking quality covers. I don't even like them really but most of their tributes are great.