I'm getting close to finishing Remake now. My one constant thought/surprise as I've been playing it is that... knowing (or hearing) going in that they've "added so much more" to the story to fill it out.... just how much it feels like the original brought to life to today's standards. There's rarely a time I'm ever sitting there going "Well, this didn't happen in the original" - and in the few cases where I am, either the events unfolding are overlain on top of a pre-existing original event (so you're not "going" and "doing" something new), or the "change" feels like it's inserted at a natural progression point that happens/plays out while you're moving from one original event to another.
The end result is that as a player, I very much feel like I'm playing through the original game, and that SquareEnix hasn't gone in and butchered it in an attempt lengthen things out. There are TONS of new things that didn't exist in the original, some more vital to the ongoing story than others, but they don't bog down the game, they don't detract from the original story, and they definitely don't leave me feeling like I'm playing a different game. Every key moment, every non-essential sequence, really what feels like every step of the original game still feel like they're here. There's just more layered in and around.