Well I just finished Quake 4 on General. I can't tell if it was harder or not than the Call of Duty games on Veteran. I actually think it probably is but the fact that you can save after every enemy you kill negates that since a lot of the difficulty from Call of Duty games comes from triggering the checkpoints.
Either way it's an insane pain in the ass when even the most basic enemies can kill you in 2 shots and over half of them have one hit kill moves/shots. Good luck if you ever try it Ronster, don't keep any weapons or sharp objects near you while you play it.