I remember three of us lugging our PCs and big heavy CRT monitors to our friends house where we spent 12 hours playing through the original Rainbow Six. I think it had lan co-op, if not it was at least the whole night in multiplayer.
On the opposite side of the scale, I once connected my 486DX 33 to my friends Pentium to play Descent over a serial connection.
As his was the fastest machine, the game played normal for him. All I saw was a game updating the screen once every 5 seconds. That wasn't much fun. π