I love games that try to find the right set of compromises to have their cake and eat it, too, in terms of combining open world feel with linear, tight narrative and deeply simulated environments.
To me Gothic was one of the milestones: One of the first large 3D open world RPGs that had a chapter structure. As you progressed the main quest line, you would eventually cross chapter boundaries that would toggle major changes in the game world, e.g. whether a given city was in front of or behind the frontlines of a conflict, altering massively who you would find there or what it looked like. While some side quest opportunities would persist over the chapter boundary, other doors would close and new ones would open. All of this did a lot to feel like the game world was meaningfully progressing alongside you, and to show the impact of your own actions on the game world.
As for Deus Ex, even the original had these "hub" locations like Hell's Kitchen, maps you'd return to more than once, in different circumstances, while also taking you all over the world to mission locations. A lot of missions had "establishing locations" where you'd e.g. walk around in a new city a bit before breaking into a corporate HQ found within it. This gave you just enough freedom to make it feel like more than a linear corridor shooter with sim elements, while in reality being planned out and guided enough you had your narrative arcs and peaks. The sequels of course expanded on this with Detroit, Prague, etc.
There's fantastic game design artistry in blending and balancing these concerns. With DX, people usually comment on the sim elements, emergent gameplay, multiple approaches to mission goals, etc., but its story and map structure is IMHO another thing that made that game so groundbreaking and memorable. The immersive sim it got from Ultima Underworld and System Shock, but this careful orchestration of alternating linear and more free-form stretches, of having character arcs, of circling back on itself and revisiting locations, of having narrative beats was new to 3D/FPS games and showed the way.
I have vivid memory of walking into the HQ of the first DX, it was my first experience of an FPS safe zone/hub area. Something felt very freeing about it, and now in later life I realized that it was being given full agency in a game. No constant combat or objective. From a hub you have the agency and breathing room to wander and explore the world building, and a good immersive sim gives you lots to find and do while you wander.
To me Gothic was one of the milestones: One of the first large 3D open world RPGs that had a chapter structure. As you progressed the main quest line, you would eventually cross chapter boundaries that would toggle major changes in the game world, e.g. whether a given city was in front of or behind the frontlines of a conflict, altering massively who you would find there or what it looked like. While some side quest opportunities would persist over the chapter boundary, other doors would close and new ones would open. All of this did a lot to feel like the game world was meaningfully progressing alongside you, and to show the impact of your own actions on the game world.
As for Deus Ex, even the original had these "hub" locations like Hell's Kitchen, maps you'd return to more than once, in different circumstances, while also taking you all over the world to mission locations. A lot of missions had "establishing locations" where you'd e.g. walk around in a new city a bit before breaking into a corporate HQ found within it. This gave you just enough freedom to make it feel like more than a linear corridor shooter with sim elements, while in reality being planned out and guided enough you had your narrative arcs and peaks. The sequels of course expanded on this with Detroit, Prague, etc.
There's fantastic game design artistry in blending and balancing these concerns. With DX, people usually comment on the sim elements, emergent gameplay, multiple approaches to mission goals, etc., but its story and map structure is IMHO another thing that made that game so groundbreaking and memorable. The immersive sim it got from Ultima Underworld and System Shock, but this careful orchestration of alternating linear and more free-form stretches, of having character arcs, of circling back on itself and revisiting locations, of having narrative beats was new to 3D/FPS games and showed the way.