...I don't agree. I think that from their australian debut up to "Back in black", they did subtle changes to their music from album to album and I always found that type of trajectory very fun to analyze and dig, far more so than artists who throw their evolution right in the face of the listener. Basically, very subtle band but I'd have no problem to explain the evolution either; each one of their 70's album introduced a new aspect to the bands sound (actually, it was often a case of what they were NOT playing rather than what they were playing). I'd say that "Let there be rock" was the big break since they weeded out the 12 bar Chuck Berry-style boogie rock songs and became heavier and more aggessive. On "Powerage" they started to expand their riff-vocabulary beyond just power-chords to arpeggiated lines and "notey" riffs on a few songs.

"Highway to hell" was of course the first album produced by Mutt Lange and was much more commercial in the sense that EvERY song needed an anthemic chorus and there was also more harmony singing. Additionally, the more minimalist riffing they often had on earlier albums disappeared too and almost every song had a snappy staccato-riff instead.

I tend to view "Back in black" as a mixture of ''highway...'' and ''powerage'' but with a new element added:refined songstructures. If you listen to that album, the songs have intros, bridges, unique riffs played underneath the guitarsolos (as opposed to just soloing over the main riff) on several songs.

They would continue to make tiny changes and e4mphasize or de-emphasize various aspects o4f their style but the popularity of ''BIB'' m4eant that they were pretty much set-not much left to do.4

This type of evolution is quite common amongst hardrock and metal-bands and may seem boring to a Radiohead fan but you have to remember that fans of this type of music take the instrumentation, dynamics and riffing-style for granted so other aspects become easier to hear.44

AC/DC is a bit extra with it though, even I can admitt that and even a lot of rockers find them too subtle...