For a remake that was hyped as "expanding Midgar" it certainly failed to deliver on that front. If anything it feels even more linear and restrained than the PS1 version.
LMAO
The only way someone would say this was the case is if they were an ultra-purist looking at the original game through rose-tinted glasses. The devs literally took locations that were just a handful of static images and greatly boosted the amount of content within each location. Chapter 3 alone took a location (the slums) that was just three top-down images with a handful of interiors and easily tripled (if not quadrupled) the amount of NPC-specific content, added in a half-dozen chapter-specific sidequests, tied said sidequests into tangible rewards (a bonus scene/choice that impacts a later chapter) and factors in the materia-specific research missions.
In fact, I'd argue that the choice system (specifically within Wall Market and via the variables that influence the choice of whether you talk to Tifa/Barrett at Aerith's house after the plate falls) are far beyond what the original game was capable of, with multiple sets of factors (including # of sidequests completed, varying sets of missions that can be tackled and the aforementioned choices in earlier chapters all changing later events.
The new locations are hardly anything to write home about, mostly consisting of generic looking factories over and over again, and every location just feels like a series of linear hallways.
And from what I've played so far, the new setpieces (the destruction in Chapter 2, Jessie's house, the first motorcycle chase and the factory raid) are just as good as the rest of the game, with plenty of entertaining NPC dialogue to match.
The ONLY time you're ever allowed to do any kind of exploring of your own is in the few chapters which let you do sidequests, which mostly consist of generic RPG stuff i.e killing rats in an abandoned warehouse, playing hide and seek with children all over town, and so on. Otherwise you're gated off from going in any direction the game doesn't want you to go yet.
The only time the content in Midgar significantly changed (before the Midgar Raid, which is just running through tunnels and collecting a couple of optional items at the Shinra Building) was on the return trip if you got the key from Mideel, and the "bonus" content there was nothing to write home about (a couple of items [Thief Glove/Tifa's weapon] and a couple of unique encounters [Cid fixing the Wall Market machine/Aeris ghost]). Beyond that, it was almost exactly the same. The sidequests and bonus content here have choices that are built into multiple playthroughs, paths that incentivize exploration [Corneo's secret stash] and plenty more to see and do throughout the chapters, including sidequests that factor into later development. I don't recall any circumstance where the devs said that Midgar would be fully open-world, and the final game doesn't do much different that the original didn't already do.