PC Gaming Eras

Pre 1981
Not really PC games but these titles laid out the foundation for later games.
Primarially text and vector graphic based games with simple input and simple goals.
1981 - 1984
CGA Era games, as well as text
1984 - 1987
EGA Era games, as well as CGA
1987 - 1992
VGA Era Games, as well as EGA. 
First sound card enabled titles through Adlib and Sound Blaster.
Multiplayer games typically relied on serial communications or a modem to a BBS type server.
1992 - 1996
VGA Era Games, Rollout of CD-ROM titles heavy on live action movies
Networked multiplayer became commonplace through IPX / SPX
1996 - 1998
First generation 3D Titles, primarially Glide and OpenGL.
Internet enabled games became commonplace through UDP / TCP, including first massivly multiplayer.
1998 - 2000
Games relying on DirectX became commonplace, Glide started phasing out.