The best thing Metallica ever did was kick Dave Mustayne out of the band, cos by doing this they gave him the motivation to form his own band, Megadeth! One of the most consistently kick arse and reliably awesome metal bands of all time.
Where as his old band Metallica have a handful of good albums and another handful of self indulgent tripe, Megadeth have a legacy of consistently awesome music only comparable to Motörhead.
And they haven't lost a single beat in time, they are still as technically sound and brutal as they have ever been! \m/