It's doom. While perhaps not as fun as the newer games, it's masterfully orchestrated arsenal and enemy roster never gets old. Can become a bit of a maze sometimes, and to be frank a lot of modern boomer shooters have eclipsed it. But few games I know aged this well.

It's a lot of fun with mods like Brutal Doom.

Doom is also a treasure for retro content, there is always something new being discovered and discussed, should it be speedrunning or the weirdest bugs. Doom has perhaps brought me more enjoyment from content related to it like impossible ports, than the game itself.