This is cute.
I like Metallica, specifically this song. When I saw that this was on my feed I was all like 'OMFG THIS NOW.' And here I am currently.
Firstly, I want to look at the duration of this song, which is just under two minutes. Sir, wut? Just kidding, this was just, as you put it, wankery so then this is more like demo or a fun thing that you just did, but besides from that, I like this.
When I put this next to the actual Sad But True, the composition and main riffs are still there, but then there are some things that you put into consideration to alter. Some minor things, like the way that you held on certain sustains, minor change-ups in particular lines that had a rearrangement of riffs.
Although, you kept more the same. Such as the entire intro, that iconic drum fill, the main riff itself (albeit, it's muted instead, an interesting differentiation). You retained the same lyrics, and pretty much, you retained the same vocal style.
I can only say so much, because of a song THAT IS ONLY A MINUTE AND FIFTY-EIGHT SECONDS LONG. -ahem- Well, I'll be leaving here after giving you 4.5 starts, the .5 is only missing because of the shortness of your submission. Otherwise, everything is right where it should be. At least, in my opinion.