In terms of games that were so advanced they almost feel like they were made by time travellers:

• Elite (1984) - procedural open world space sim

• Ultima VII (1992) - full NPC schedules, open world and day/night system so you could rob stores at nights, follow people, etc. and awesome exploration. In 1992!

• X-COM (1994) - a voxel-based LOS system, destructible environment, z-levels, natural elevation on terrain (deforming the isometric grid), reaction fire, etc.

• Daggerfall (1996) - a faction system, procedurally generated areas and quests, a lot of options to get to different areas (climbing, levitation, etc.)

• Thief (1998) - a full sound simulation with different materials having different properties, the ability to extinguish torches (dynamic lighting!) and cover metal surfaces, a light system for visibility too (now commonplace).

• Baldur's Gate (1998) - a semi open-world AD&D2e implementation - with co-op multiplayer! (most modern games don't manage this)

• Deus Ex (2000) - a branching FPS/RPG campaign where choices matter with a basic stealth system and lots of approaches to each level. It was basically a completely modern game out of nowhere in 2000.

• Runescape (2001) - one of the first major graphical MMORPGs with a full player economy.

• Morrowind (2002) - a fully 3D open world with a lot of options for magic (including custom magic) and exploration.

• Hitman 2 (2002) - first stealth-focussed game with a full disguise system, map, etc.

• Oblivion (2006) - like Morrowind but with some NPC schedules (like Ultima VII), a stealth system (based on Thief) and Havok physics based traps.

• Red Faction: Guerrilla (2009) - fully destructible buildings and environments in an open-world campaign.

Those are the ones that really stick out (also Super Mario and Zelda on consoles, especially the SNES, N64 and recently on the Switch handheld). It's a shame that the rate of progress seems to have slowed down a lot at least in terms of ground-breaking features and simulations.

But who knows maybe Baldur's Gate 3 and Starfield will both be on future lists like this.

Ultima VII really sticks out as just crazy though, that game could have released 10 years later and held up.