Some famous musicians, most notably Dave Mustaine (for obvious reasons) have long complained, criticized, or said that Lars isn't a good drummer, maybe decent-to-adequate at best. He's a great, extremely sharp, savvy businessman and to be fair, he's probably responsible for 85-90% of the financial, creative success Metallica has enjoyed and accrued since the mid-late 80's.
Also, Lars has to be credited for essentially keeping Metallica, as a band, together because after Cliff Burton's death, the surviving band members were not in a good mood, James was, reportedly, extremely depressed, they were still deeply mourning Cliff's death, and oh, by the way, they had a Japanese tour scheduled in less a month and they had to hold auditions for a new bassist, which again brought back sad, depressed, very raw memories of Cliff's death. Lars had to sort of become the band'a leader, by default and despite some noted criticisms of him over the years, some of it deserved perhaps, but if he doesn't step up and keep the band together, metal fans never would've gotten And Justice For All, the Black Album, Load and Re-load.