There's a valid argument that at a glance the game is roughly the same as the original. In a world where people expect considerable graphical improvements or slight improvements coupled with gameplay overhauls Destiny 2 isn't impressive to some people. Destiny 2 is launching on hardware D1 launched on and the gameplay is pretty much the same so it's easy for me to see that. At a glance a casual fan will easily mistake D2 gameplay footage as a D1 expansion.
While I like the new planets, other additions and changes Bungie's making I can't but feel a little disappointed. If they're going to be ballsy enough to call it Destiny 2 there should've been more to it than the game simply being more of the original. Yes the game looks slightly better than the original but it doesn't stand out that much in YouTube video on my PC monitor. (Maybe it will at home running in real time on my own TV? Can't tell yet.) And virtually all of the gameplay shown isn't far from the original and it's expansions. Yes, when you boil it down to a list of bullet points the changes and new stuff amount to more than the previous expansions combined but that just means this is could be considered a huge expansion.
Quite frankly, I was expecting big changes. Stuff you would expect in a big sequel like changes to playspace structure (such as jumping from confined zones to an open world map), removing Strikes and replacing them with bigger and better adventures, losing the spam-tier bosses that dominate Strikes, improvement of vehicular gameplay, reinvention of the subclasses, new elemental categories beyond the original 3, etc. That's what I expected when they announced Destiny 2. Now I don't hate what they've shown so far. I can appreciate the QoL improvements, new enemies, and weapon types. I just hope that they have more for us.
And I wouldn't give too much shit to people complaining about architecture. There's all kinds of human architecture today in real life but Destiny 2 seems to carry over the same Vex, Hive and Cabal-style structures from the original. It's a little boring and doesn't help the game stand out. Along with their habit of recycling content during D1's life, the returning architecture styles are probably another reason why they keep emphasizing that these are new planets and zones.