Actually, to be honest I don't think that it has the same amount of content as NL / previous titles precisely because of the things you listed below with furniture/special NPCs/upgrades/unlocks and other "progression" aspects of the game. The original purpose of the game was a sort of socialization-centered, slice-of-life progression. NH did indeed add a handful of things. Namely terraforming, which is certainly unique and meaty as far as features go and has led to many beautiful usages, though it might not be everyone's cup of tea and seems to lend us the power to micromanage each and every detail of our island which was never really the point of previous games. Crafting too, and being able to villager "hunt" of course, placing things outside.
But many older players still feel like the game is severely lacking because it seemed to REPLACE all of the unique facets of the game that they particularly enjoyed, rather than enhancing them. The game would've felt not only equal to past titles but extraordinarily ahead of them if it had had these features IN ADDITION TO all of the unique and staple NPCs (the pelicans for instance, the police dogs, Tortimer/Kappn/Brewster/etc), the older distinct features like gyroids and et cetera, the robust socialization aspect (socialization is certainly a BIG problem in ACNH, seeing that the villager dialogue isn't too diversified and the personalities have been extremely watered down) and the unlocks. Sure, there's a few "unlocks" still in the game, but they aren't very hard to overcome. Progression-based gameplay seems to be cut short in the game. We don't even have the ability to upsize the outer rooms of our home.
The vital and detrimental mistake that Nintendo made that rightfully left a bad taste in so many people's mouths is they thought that these new features could REPLACE the unique staple features/characters/functions that made so many of those people fall in love with the AC franchise to begin with. They are fine features, Minecraft and Sims-esque or not, but they should've enhanced the game experience rather than serving as a replacement.
The update will hopefully bring it up to speed as far as the older and widely beloved features go. Unfortunately many things still seem to have been left behind or rejected from the title. For many older players and for those who are moreso fans of the original aspects of AC rather than the new design/customization aspects, this is a bit of a disappointment and in my opinion a very understandable one.