Those are gonna be just my opinion, so take it with a grain of salt. Note, this is not gonna be about the lag/server/maintenace issues that NGS is undergoing, but precicely about the game and gameplay it'self.
While I love the concept of the Open world, I just sometimes miss the more simpler and more sandboxy feeling of the original PSO2, where we could easily pick any quest or challenges from the counter and the game would throw us up quickly right into the rage of combat.
I realise that when PSO2 was initialy launched on the JP side 8 - 9 years ago and did not have content, but I am sure it had decent amount of starting available Fascion items/cosmetics and Outfits/Uniforms available. I'm not gonna start with the gear of the player because I dont think this is of importance, but I think NGS entirely lacks in content when it comes to the fashion aspect, the "Soldier Line" doesnt provide anything interesting for me, and the amount of NGS starting default outfits available is almost complete null compared to the base PSO2.
To be honest, I dont like how the way the Story mode of the game is handled, I liked it how it was in the base PSO2 where the singleplayer storymode was separate as a series of story quest to be attended in the counter. But NGS now forces us to progress through the story missions just to unlock all the shop or menu features which should all be unlocked from the start. On a side note, I dont really like how the story is getting approached here, it tries too hard to be like a cinematic movie and not retain what it was in the original PSO2 where everything felt more like an Anime, NGS just feels too much like It tries too hard to be like the Jumanji 2/3 Movie (Not saying I hated that movie, I actualy liked it, I just dont like how NGS doesnt really feel like an Anime and more like westernized hollywood cinematic movie).
This take would most likely be wrong, because in base PSO2 I have been mostly an Phantom/Braver player myself, since those classes had one of the most fast paced playstyles, but still hear; NGS combat just feels extremely slow-paced and clunky to me, It could be because of the lag in the game but still it feels slow. I know Fighter is fast paced, but I'm not interested in Fighter because it does not have any weapons I'd interested in trying to play, especialy because this class is very squishy. I just look back at PSO2, I would play with the braver, I would quickly maneuver around and slash everything into pieces with lighting speed and then continue blitzkrieging rest of the enemies in the area, the combat overall felt fun, fast-paced, flashy and arcadey, I just dont get the same awesome adrenaline pumping experience in NGS, the combat just feels so slow and boring, we are limited to long charging times of the photon arts/Techs and spamming them all over and over again.
Maybe SEGA decided to approach the game with more cinnematic tone with just how the gameplay feels like and the cast of Characters , but I feel like this is a step backwards of what PSO2 should be.
To conclude, I honestly think that the game would be most likely "Crowded" for 3 to 6 days, untill all players will reach level 20 and obtain all the high level gear, after this majority of the players will realise how the game lacks content, and the game will turn into a Ghost town quick. SEGA in my opinion needs to address the major issues with the game and the lack of content.