Metallica should have ended their career after "Justice for all", or, at least, renamed their band because it doesn't fit right with the music they released afterwards. Neither did their attitude.

You can actually see this evolution (rather: devolution) even on their first 4 LPs. KillEm All was still rough, not well produced when a young band that sometimes even didn't have a proper sleeping place still were searching for professionality. Ride the Lightning set the gold standard for the production of a thrash metal album and the sound of a (then) modern aggressive e-guitar. Master of Puppets increased their skills in writing interesting songs with more complexity, but with Justice for All they already tuned down the aggressiveness in production down, esp. e-guitar, drums, and speed altogether.

Then they became a complete commercial rockband that could be played even in radio...

Well adding to this I found out that they had a few of Dave Mustang songs laying around. This caused inspiration for other songs to make albums untill they ran out of them after justice for all. That was when they decided to become a blues band, and later a alternative band without solos. This being true firing Dave was a mistake, but without firing Dave we wouldn't have Megadeth. They need a Metal consolidator bad, but instead we get titty bopper groopies; because their are more on the planet than us oldies. Ironically; because of their age they would listen to anything you tell them it's cool due to advertising that is why most true Mettalica fans walked away after the Black album. With Lars giving us a good excuse telling us that we will listen what ever they put out no matter how it sounds.

About thrash it is better that death if you take the reclassifying of thrash bands as death. Speed metal is also better than death. With older bands retiring, and record labels interfering with music they have lost a lot of gutarists. Can't really knock the new gutarists; except, they are not as skilled as a lot of the thrash, and speed gutarists.