Forgot Wing Commander and Wolfenstein 3D ;p

Quite an old one. Nevertheless here is my advice of the best:

2D Platforms: Abuse, Another World, Blackthorne, Dukenukem 1&2, Flashback.

RPG: Albion, Anvil of Doom, Elderscrolls Arena, Jagged Alliance, Syndicate

Sims: Comanche 3, Gunship 2000, Falcon 3 (outdated)

Scrolling Shooters: Raptor Calls of the Shadows, Tyrian 2000, Death Rally (sort of)

Strategy: Dune 2, Enemy Unknown (XCOM1), Terror from the Deep (XCOM2)

FPS: Doom 1&2, Heretic, Hexen, Strife (forgotten diamond. go for it plz), Duke Nukem 3D, Shadow Warrior, Redneck Rampage, Quake 1&2, Descent 1&2, Blake Stone 1&2, Blood, Chasm the Rift, Eradicator, Powerslave, Realms of the Haunting (best, biggest, longest and hardest horror fps ever made), Star wars Dark Forces

Dont forget MDK and Crusader series

Cheers!!

Wolfenstein 3D. The father of it all. Next Doom, Duke Nukem 3D and Chasm - The Rift