Metallica ¿Are a Progressive Rock Band?

I really can't stand thrash metal and yet I am or at least used to be a big Metallica fan.  Growing up, I never really considered Metallica to be a thrash band.  Of course, people here on PA refer to Judas Priest as a thrash band and I never considered them to be thrash and they are one of my all-time favorites.  My idea of thrash back in the day was bands like Exodus, Slayer, Venom, S.O.D., and Overkill, which were generally all bands that I didn't really care for.  And Megadeth was kind of a bridge between Metallica and thrash.  IMHO, the only Metallica album that I might consider as a thrash album would be their debut Kill 'em All, and maybe some of the songs on Garage Days, otherwise they were kind of a one of a kind heavy metal band.  I bought Kill Em All and Ride the Lightning LP's shortly after Ride the Lightning was released from an advertisement in a Heavy Metal magazine.  To my mind, Metallica were playing a brand of heavy metal that noone else had really ever played before.  I don't know that the idea of "progressive" metal would have existed at the time, but looking back at it now I would say that yes, Metallica "progressed" heavy metal and I believe that they are one of the major influences on progressive metal.  Not being a musician I don't know much about time signatures and complexity of playing so I have no input from that point of view, however, one of the major things that impressed my friends and I about Metallica is the way that they did change the time signatures within a song.  Not being musicians maybe this was just an illusion but that was definitely the impression that it left and was one of their main appeals.