I have also been very impressed by the performance and fluidity of Doom and Doom Eternal. Even when playing from a HDD (on a computer made from leftover parts), when high res textures and geometry didn't load fast enough, the engine just showed a low res version before smoothly blending to higher res without ever stuttering. It's a minor miracle how well these games run, even on GPUs 2-3 tiers lower than most others require.