lol ok I'm gonna go ahead and say this at the risk of sounding like a complete Metallica fanboy.
I mentioned in another thread that I feel that Metallica are masters at constructing songs. They can create a song that, while it never strays too far from common song structures, remains fresh and unique after decades of over-listening and over-playing. They've displayed this talent since Kill 'Em All (not so much recently, though DM was ok). I'm a bit surprised by some of your opinions, as Metallica in these early days had a very noticeable progressive influence (again, they've exhibited this influence in their songs since their debut). Also, the riffs...I need not say more about them. They are an example of an objectively "good" metal band imo; you don't fill large arenas on word-of-mouth and limited radio airplay alone if you're a band that only some people would enjoy (like Opeth)...and they were doing this before their major commercial breakthrough (The Black Album). So, to answer your question, I don't feel they're overrated...they are justly and deservedly held in high regard.