Thanks for the let in, I'm sad that I missed Dimmu Borgir on my list, they were one of my first metal bands...
I agree that most artists feel they need to innovate over time to stay fresh and cool (and also to make money), and plenty of bands have done that. The difference is in quality.
For example, I like new Dark Tranquillity as much as I like thier old stuff.
Some things stay kind of the same, for example, Lamb of God (even though they are kinda new, they still put out 3-4 cds [depends on what you want to count] and all are similar but all are good)
Some bands get worse, and I think Metallica is one of them. St. Anger isnt complete trash, but it sounds nothing like the olden thrash metal of the 80's (aka the stuff I prefer) and it feels like an attempt to be more mainstream, just like the black album, except for worse.
The same reason is why I dont like new In Flames, it just isnt as good after Clayman.
Just my opinion.