Just to say, this is a difficult game to love, as much as I wanted to in it's released form... However, having written this was unplayable in my posted review earlier here, I finally got to take more time with it... It could use an update, to cover those optimizations that are listed as work-arounds at it's pcwiki's site; but then, for the jittering, etc, mentioned here, the advice there does help.
There are 2 useful mods I also know of now, that help the experience; both at moddb website: 'Unwrath-Aeon Of Fun' and a new 'multiplayer and coop' mod recently posted there. The multiplayer is still in beta, but released, and includes a better separate single-player mod I am using -- swaps the jump and fire mouse buttons, helps with this for me anyway. Lol. And the game just generally runs better. Both mods I tried there were an Improvement; and the 'Fun' mod leaves the layout of buttons alone, but also helps with normal jumping and physics (as both do); and both leave the original game intact so far as I can tell, and I have progressed some ways into it for a change, and find it now to be more what I was hoping for... So, I thought I would just post this recommend to anyone else struggling with this as I was: I hope this Helps; and, ENJOY! :-)