Wuchak
Dynamic documentary on the first 25 years of thrash metal
Get Thrashed does an excellent job detailing the history of thrash and other offshoots of metal up to the time of its release in 2006. Generally speaking, thrash combined the double bass drumming and complex guitar riffing of NWOBHM bands (including Priest and Maiden) and fused it with the aggression and speed of punk/hardcore along with the technicality of prog bands. The documentary relays all of this in a very energetic fashion, including references to the most prominent bands, along with myriad commentators.
The Big Four are, of course, noted at length, but myriad second tier bands are acknowledged, like Overkill, Death Angel, Forbidden, Sepultura, Hirax, Kreator, Sod...