It's a good album. I don't care if it sounds like their earlier stuff; I care if it sounds good. I didn't care that RTL didn't sound like KEA, or that MOP didn't sound like RTL (despite a fair bit of similarities), or that AJFA didn't sound like MOP. So why would I care if DM doesn't sound like any of those albums. Metallica is one of few bands from the "age of thrash" whose sound and direction changed significantly from album to album, and that's part of what earned them so many fans. If anything, I'd say the similarities between MOP and RTL are what keep fans hoping that Metallica will "return to their roots" and make something along those lines. But it was really only those two albums which had any strong similarity. Pigeon-holing the band to those two albums is a bit ignorant in my opinion.
Arguing about what's "true thrash" and so on is ridiculous. Who cares. Either you like the music or you don't. Especially when half the people arguing what's "true thrash" or not are in their early to mid 20s and didn't grow up around the "thrash boom" in the 80s. While we're at it, let's talk about what "true punk" is. That's an argument full of equally pretentious pontification that spans a couple more decades yet.
Jugg, you can stop hanging off Gary Holt's nutsack already.

I like Exodus as much as the next guy, but this music was never meant to sound like Exodus. I like this and I like Exodus too...because they're different. So sue me.

For that matter, the Police's "Synchronicity" is still one of my all-time favorite albums. I bet that blows everyone's mind...
As for whether this album will become a "classic" to me, how the hell would I know. It's not 2028 yet is it. Someone mentioned listening to MOP recently and getting goosebumps during certain parts (perhaps it was in the similar thread on HC). Well yeah, with all the nostalgia attached to the album by this point you may get goosebumps if the album still "does it" for you at all. But imagine an album in that style being released today. I have a hard time believing that the younger crowd would eat it up the same way they did when MOP was released some 20ish years ago. As for whether they'd be able to give their old-time fans goosebumps...good luck with that. Talk about a double-edged sword. Trying to recapture a sound they had 20+ years ago means risking the appearance of blatantly copying past material. Again, every previous album they had didn't sound like the one before it. Specifically going for the "vibe" or "sound" of one of their past albums now would be a death knell for them.
Here's how I look at it, in a nutshell: here's another good album for me to add to my collection. I can pretend the last 17 years of Metallica didn't even exist if I want.

And since I haven't even written one song in the last 10 years let alone an album, I'm thankful there are bands that still make music that I can appreciate enough to buy (whether it's an old favorite band or a band I'd never even heard of). Trying to hold Metallica up to some measuring stick of their past albums which are heard with nostalgic ears isn't something I consider reasonable.