After Doom there came Quake. Quake was much lauded because of its highly ambitious 3D graphics (a world away from its predecessor) and the new-fangled ability to play multiplayer games over the internet (a novelty back in 1996).
All of the games in the Quake series are available as a download through the Steam network. Still have the original CDs? You can run Quake on Windows 7 by copying the game folders from the disc and manually running the setup/install.exe.