Exactly. Portal 2 is no doubt a fantastic puzzle game. But so is Myst, and Myst did a lot more with a lot less technology.

Calling Doom a novel approach is a bit of an understatement, don't you think? Doom is easily one of the most influential milestones in the history of video games, period. Despite the roughness around the edges -- most or all of which was necessary to get it to even work on PC hardware of the time, as it was certainly well understood by hyper dimensional time traveling space wizard, John Carmack. Nowadays we all know how the engine cheated, wasn't truly 3d, and where all the jank and bugs can be found. But from the perspective if someone in 1993 playing on their 486-DX, Doom really felt like a highly polished and complete experience.

Doom's impact in the scene in 1993 was so vast that you can still see it to this very day if you know where to look. There was so much that it either invented or perfected: Network multiplayer, both deathmatch and co-op; the now standard FPS loadout of melee-pistol-shotgun-rocket-launcher; the entire modern concept of the "violent video game" controversy; the notion of rock star game developers (John Romero...); the capability of generating distinct and recognizable 3D environments with a sense place. That's really just the start. Doom made the entire video game industry at the time do an about-face. It changed the landscape forever despite how quaint it might look today.