In the end, while it may be a huge cop-out, it really does come down to personal preference. Some people will simply not be able to handle the huge downtime between pulls, not being able to buy a new skill rank because you spent all your money on food and drinks (mages were popular for a reason back then), the very slow pace of leveling, and a whole lot more frustrations and not user-friendly features. On the other hand, the experience really is significantly different enough from modern WoW that it does feel enough like a "new" game, or at least a new and different expansion. An expansion that has many more differences than the last 3 or so, something that's both new and old and familiar. And, yes, it also offers massive quantities of nostalgia for those of us that played Vanilla, but what's so wrong about that?
The simple truth behind all of this bickering and squabbling is that there really isn't a bad way to enjoy a game. You like the feeling of Classic taking you back to your young(er) days and that rush of falling in love with WoW for the first time? You like the slower pace of both combat and leveling? You like that the social aspects of the game take a front seat? Good, enjoy it! You prefer modern WoW and BfA with it's tons of improvements, smoother design and more player-friendly features? Great, enjoy it! It doesn't matter whether you prefer modern WoW or Classic or WotLK or whichever your personal high-point was (it was Burning Crusade and Legion for me), you're not wrong. You literally can't be. No matter what anyone says in all these heated discussions, they care about WoW, in whatever form they prefer it. So why can't this be enough of a commonality for us to have a civil discourse?