Terminator: Future Shock
>large outdoor maps designed around exploration and atmosphere, predating Turok by two years and Duke Nukem 3D by a few months
>fully-polygonal texture-mapped enemy and character models and environments, predating Quake by a year
>took full advantage of mouselook aiming, once again predating both Duke Nukem 3D and Quake
>fully-interactive, driveable vehicles (including an aerial vehicle), predating Tribes by three years, and Goldeneye with its tank by two years
Hunter
>One of the first sandbox/open world games released in 1991, predating GTA1 by six years and Body Harvest by seven years
>polygonal graphics (albeit not texture-mapped)
>fairly solid variety of drivable vehicles for land, air, and sea, along with weapons
>almost every building in the game can be entered
Haven: Call of the King
>ambitious variety of gameplay formats, primarily being an open-world 3D platformer (not a particularly good one, but still)
>seemless space exploration, allowing you to fly an aircraft towards the sky, go into space while seeing the environment below you fade out to a planet, and travel to different planets in real time with little to no loading screens, similar to what Free Radical was attempting with their cancelled version of Star Wars Battlefront III
>does many neat hardware tricks with the PS2 to maintain its sense of scale while running at 60fps
These games are far from perfect, and definitely show their age, but I think it's a shame their technical accomplishments and design ambitions aren't spoken about more often. Post more games you think fit this category.
Starfighter
>fully destructible environments, including some rudimentary terrain deformation
>fully texture-mapped polygon graphics, with an impressive draw distance and sense of scale, maintaining a playable framerate on a console technically-inferior to the PS1 and Saturn
>can travel into space at-will by simply flying your ship towards the sky, though this doesn't include interplanetary travel
inb4 Skyrim and Toddposting jokes