Most of the story beats are still there. Most of the emotions from the OG are still there - except one thing. I'll try to avoid spoilers but if you've played OG and remake, you should know.

The major change in the story itself is the continuation of something you saw at the very tail end of the first Remake, that probably made you go WTF, the meta-narrative you're suspicious about. It might be a concept you don't really like because it sounds like it'll break the story, but it actually doesn't concretely change anything until the end. The places, the events, the world, the mission are still the same. The most critical change that caused a lot of noise is a big cliffhanger that will only be resolved in the final game, when it was expected to be a big emotional hit now. It's very clear that this is a trilogy, and expecting this game to end the same way as the OG caused a lot of distress. People who loved the OG for one specific reason or another might feel robbed by the way this game is pretending to change things, but actually doesn't, but actually maybe yes - and you'll only get the resolution in the last game. If that means something to you, maybe you should wait for the trilogy to be completed and treat it as a single game, because this part 2 is only half of the game you liked back then, and it might not have what made you love it - yet.

One big change in storytelling is what it focuses on: it gets much more into the psychology of Cloud, Tifa, Aerith, Barret, about mental health, trauma, and their relationships (in the same way they massively developped the Avalanche trio in Remake). Basically, they're making everyone real human beings with a history and interactions. Now you understand from the inside of their head why they do or don't do this or that. It also adds focus on some aspects and perspectives that only developed in the Crisis Core prequel and were not a thing in the OG. It's a massive improvement on storytelling and world building (the world now has a history of geopolitics scattered everywhere in every side quests), but it looks like a lot of fans of the OG who expected things to go a certain way get hung up and slowed down by all the new details, and it feels like fluff or a change they don't like. You clearly feel the stretch from one 50 hour long turn-based RPG into 3 action RPG that last 50 (remake) + 120 (rebirth) + 1?? (part 3) hours, and it's a lot, and you might not like it.

It absolutely has tons of gaming content to enjoy, both in the characters and the absolute shitload of things and side quests and mini-games to do absolutely everywhere for a 120 hours playthrough and you don't even see the time pass, but it might not be exactly what you felt in the OG. It's a new perspective. I've seen among various streamers that the people who were the most confused by the ending are often the harder fans of the OG, and new fans see the details and hidden explanations that OG fans miss because they think they know what's going on - and get blue-balled on what they came here for.

And then Sephiroth changes. We still don't know if they're whitewashing him by giving him a sad backstory and a big personal mission (the gacha game Ever Crisis that's still ongoing is developing his time as a young SOLDIER) or if they're making him an even worse guy, and so far it has the potential to ruin the character. We have to wait until it's all resolved.