The level design is literally the original game + a bit of extras. Trust me that's not why the game got hated. People who were hoping for GTA level midgar open world were deluding themselves, that kind of game wouldn't be a remake at all because it'd be impossible to control the narrative pacing.
Look... I alluded to this on NerdoGaf.
FF was one of the three IPs that made me appreciate videogames as an art form (MGS3 and Silent Hill 2 were the other two).
I see FFVII/VIII/IX as a whole, so I will talk interchangeably between them.
Those FF games for the original PlayStation are still so incredibly ambitious; they pushed the medium forward... It was as if Square Soft was so far ahead of everyone else that even the PlayStation hardware was too small for them. This is why they had to use FMV mixed with real-time 3D in some sections of the games. And we could continue discussing each element of the games.
Now....i will not subscribe to the reasons of why other people hate or not FFVII remake or/and each Final Fantasy from Square Enix.
I have MY own reasons.
to address at the points of you made:
"The level design is literally the original game + a bit of extras"
ok. We could talk about level design from a cognitive and even philosophical way. we could argue that it dosen't matter if the level is literally a corridor or a huge wide open area; the player is always engaging in straight lines. (the length of these lines varies).
when you look at those old FF games, they are basically still frames (pre-render backgrounds) with usually one to three options to trigger the next screen.
To circumvent this drawback you had changes in perspective between screens. this introduces visual variety and even visual storytelling (Exteme Long Shots > full shots)
another thing that those old games have is the cleanenless of the screen (No HUD or wave points) and a very heavy reliance on the music to enhance the immersion and mood of the place.
But even with so many limitaions you felt you you were actively exploring the place.
So, FFX, XIII, XIII-2, VII remake and XVI have basically none existent level design; corridors galore with a very obvious repetitive layouts. Add redundant Wave-Points and checklist and you have mindless exploration.
what is an example of superb level design? The Last of Us (especially the first one).
Beach (straight line)
Sewers (L shapes)
Suburbs (S shape)
"boss fight" sniper.(H shape)
It's baffling to see the level design of FFVII Remake/XVI resembling that of the early PS2 era. They feel sterile and artificial.
let's remember how hard was for Japanese devs to transition to the "HD Era" but for Square Enix, this struggle started in the PS2.
which relates to your next point :
"People who were hoping for GTA level midgar open world".
When you look at how FFVII/VIII/IX handled the concept of an 'open world,' you quickly realize how constrained and directed they are. yet, they managed to evoke the sensation of an entire planet within the game—a true globe. I was mind blown while exploring the map with the airship, heading north, and suddenly appearing at the opposite extreme just at the edge of the world map.
this feeling is entirely missing in SE FF games. which is one of the most iconic and memorable moment in any FF.
and this is the main issue with Square-Enix: Bad Management and poor R&D of Technology.
It is due to these issues that they haven't been able to achieve what people expect from a game called Final Fantasy. This is why each installment from Square Enix has been divisive.
To tie this back to the thread: It is widely known that despite the benefits the Creation Engine offers for the type of games Bethesda produces, it is also a significant reason why Bethesda's games are often plagued with bugs, jankiness, visual issues, poor A.I and immersion-breaking loading screen.
Just as many people here use one of two lackluster or missing features to shit on Starfield (which you could see as justified or an exaggeration), like not been able to fly on the planets...the same energy must be kept while defending or criticizing another game.