It used prediction and delta codes, and actually ran the server and client (and still runs) at 72 fps, no other online multiplayer game that I know of has done it ever since. This means if you have ping 14 milliseconds, you really have ping 14 milliseconds.
If you've played Quakeworld with solid 72 fps (this only really became possible many many years after its release) and a good mouse, monitor and decent internet connection, all other games after that feel like clunky puppet shows where you can only vaguely affect the end result. That's the reason why it's still being played. It really feels like you're on the server.
The game also enables amazing moves that can be pulled off by sufficiently skilled players - there is no roof for domination abilities, There can be tens of levels of players that can crush anyone below them easily. This also means that it can be pretty newbie hostile at the same time. But it's pure bliss when dueling with someone your own level.
The game companies assumed (probably correctly) that the average consumer never pays attention to good control or stratospheric skill potential, and rather pays for the resolution, level of detail and nice colors as well as newbie entry easiness.
So, Quakeworld was and probably will always be a one off with no peers, a raw formula one in the world of soft SUV:s.