Uncapped framerate is a feature implemented by various source ports that removes vanilla Doom's hardcoded framerate cap of 35 frames per second. Whether this is a positive thing in Doom has been disputed, most commonly because the feature has been said to hinder the mouse feel.
Source ports that feature an uncapped framerate utilize view interpolation, which in turn produces lag into the mouse response times. Whether this effect can actually be felt in the controls to the extent of being a nuisance has been disputed, other players claiming they do not notice any difference and others arguing the effect makes the mouse control distinctly worse.
Further criticism includes the feature causing motion sickness and increased eye strain.