Even as someone who isn't that big on Death Magnetic or Hardwired (though the latter I have only listened to a few times) I don't think this new single sounds amazing or anything but it sounds perfectly fine for what I expect. If you put things into perspective, this will only be Metallica's 11th album in a 40 year long career and it's crazy to think that Rob has been in the band for 20 years now and this is only the third studio album he's a part of. They made as many albums with Cliff in 3 years as they have with Rob in 20 which is kinda funny to me.
The song does have some Kill Em All vibes, and while it does sound a bit 'like expected', I feel like maybe it was just a safe choice for a single. There could be more interesting songs on the album, at least I hope so, but it also makes sense to just release something short and to the point. Especially considering how kinda 'bloated' their songs have been on the last 2 albums. It also feels like a new Metallica album is just a reason to go out on tour again, play the songs people want to hear but also add some new songs in the mix to keep it interesting for them as well. It must get pretty boring playing the same songs for all these years so I'm sure having a few new ones makes a difference.
There's plenty of other bands who have been around for decades who churn out albums that aren't as good as the classics but they're still 'doing their thing' and pleasing fans whether it's DT, Iron Maiden, Deep Purple or so on, I don't see why Metallica should get any flack for it. I remember a huge gripe I had with the band was that they weren't prolific enough. I had to wait years for Death Magnetic and then Hardwired was basically another decade after that. Even if this ends up being a 3/5 album or something, it's nice to get something.