All of my favourite 'tallica stuff was done early in their career, but that doesn't mean that I won't listen to newer stuff. A band that's been around as long as Metallica are in the impossible position of either putting out the same sounding record until they call it quits or trying new things and risking alienating their established fanbase.
I'd rather have a band that stretches and challenges itself to grow than listen to the same E minor pentatonic riff for the rest of my days.
Different strokes and all that.