Mimicry can be a form of flattery. Metallica's influence has been enormous.

When I had a job and more money I was a crate digger. James Brown, Funk, Soul and Hip Hop were on the menu for me. Copyright was never a big issue until "Paul's Boutique" by the Beastie Boys was released.

If anything a few of my favourite bands, Coroner and Gore were heavily influenced by Metallica. The Avenged Sevenfold track sounds inspired enough to be fun. Not Pantera or W.A.S.P fun but good for "hmmm, nice for a single listen".

When band A rips off band B and gives credit to band B, cool. When no credit is given where credit is due, not cool. The worst rip offs are bad rip offs. I prefer the Metallica track as it sounds more Metal for me. Avenged Sevenfold sounds a bit "meh" but at least they rock.

One Direction's rip off of the Who's "Baba O'Riley" did make my blood boil. No credit was given to The Who. Pete Townshend was okay with them using the sound of "Baba O'Riley" yet I still think he and the Who should be credited.

Rip offs are a subjective and complex matter. Horrible ones are on my list of music to ignore...

Instrumentally the songs were identical despite Metallica having a different sound and heavier sound. Hence the word "mimicry". Thing is if imitation is not emulation, then is it immediately  ?

Often I would say yes. I was once at a Linkin Park concert. It was actually Dead By Sunrise with Chester of ... but I still call it Linkin Park and yes I was only slightly entertained. The best part of the entire concert was meeting two random metal heads and talking about other bands, solos and whatnot.

After the concert I came to the conclusion that Dead By Sunrise was still a Linkin Park rip off and thus . When imitation is not emulation in some way, it is worthy of ignoring.

Later admitted infringement by Ghostbusters' producer, but thank God they did infringe. The Ghostbusters version is far superior.

Led Zeppelin are legendary song stealers.