I'll have to give this a try. Maybe it's a nostalgia thing, but Doom feels "wrong" at higher resolutions and hardware-accelerated texture smoothing. In the past I usually set GZDoom to a 720p resolution with software rendering while disabling up/down mouselook. This to me is the best of maintaining a "classic" Doom feel while still supporting widescreen.
However, the software rendering in GZDoom does that 256-color-only fade out thing which really contributed to the scary, gritty look of the original. Game looks "better" with that enabled even if it's not truly 3-d rendered.
That's the awesome thing about GZDoom though. Everyone can make it their own game and customize it how they want. It's fascinating people are still making new levels for it.