Perfect blend of nostalgia, aesthetics, gameplay, simplicity not to mention that id software releasing everything open source at the end has continued developme

Perfect blend of nostalgia, aesthetics, gameplay, simplicity not to mention that id software releasing everything open source at the end has continued development and created a massive amount of third party content, mods, etc. The same applies to Doom, Duke Nukem and to a lesser extent a few other older fps games.