For me it's not really the aesthetic, but the gameplay in itself. Doom 1, 2 and 64 were, understandably, very different from the other parts, but very similar to each other - a game based on movement, where you fly around the map at ludicrous speed shotgunning everything in a few hits. Doom 3 is much more tactical in its game and weapon play. You aren't just infinitely fast and can save yourself from every situation by strafing, but you actually need to use all your weapons as they are best. Doom 2016 was a perfect mixture out of both styles, with high speed movement, (double) jumps, and a use for every weapon for its unique abilities. Everything was nicely integrated and balanced. Doom Eternal not only changed that style again, they also removed many good concepts, like classic maps and runes. It's clearly a step down, in almost every way, and yet another gameplay style.