Quake 1 was worth it even if just for the multiplayer. It was so good that people were having fun online even on just the "start" map with the shareware version. Quakeworld was especially great and very playable even with a modem. Then you add the moddability (including QuakeC) and the groundbreaking renderer, it's one of the biggest technical achievements in gaming history.

The single player was weaker than the multiplayer, but still enjoyable with its strange variety of map atmospheres.

I'm glad Quake happened even if it made id Software a worse company thereafter. I would understand if the people involved feel differently though.