Dude, I'm not even that big of a Metalica fan but back when they came out that s#$t was a revelation. I'm not trying to be condescending when I say this...you're just not old enough to understand what type of impact their music really had at the time.
Its kind of like when Nirvana got big. The whole music scene changed almost overnight. Every thrash, black and death metal band you hear today is either influenced directly by what they did or influenced by a band that was.
Also, keep in mind that at that time metal wasn't nearly as palatable as it is today. They built themselves up to the point where they were selling t-shirts in freaking Sears when And Justice For All came out with virtually no radio play.
Give him some props. He is considered good because every song he played on, whether he shined in it or not, was part of a revaluation or sorts. It also doesn't hurt that he died in such a f&*#ed up way.