Classic Online shooters you wish were popular again

What are some classic online shooters, that you wish were popular once again? I think Quack is a big one, but Unreal Tournament is another that comes to mind. Those are the top ones I can think of. What are some FPS online shooters you wish were popular again?

I would say Doom but I think Doom has always been popular! Quack was fun back in its day. Halo used to be really popular when it came out. It has really died down since then so I would say if Halo would become popular again that would be good.

I won’t mind seeing some come back from quake, I only had the chance to play quake 4 and I loved it.