Thanks! Glad you like it 
I made my own thick layer on top of JME and I use the akka-actors framework to run all the game logic (incl. physics) in a separate thread(s). I described my process here:
This game is based on that framework.
Specifically for the movement (which I rewrote since that old post) I took a different direction than the common player controller: Instead of a capsule I have a “flying cylinder” and I ray test downwards to measure the distance to the floor, if too high I calculate the acceleration and move it down, otherwise I move it up (steps). This basically overrides all the bullet physics for the player movement with my custom movement.
It’s surely not physically accurate but it feels so much tighter to me and I avoid some problems like unexpected jumps on steps and sticky walls (but I miss riding platforms which I plan to implement).
I used the original quake source as reference so I can strafe jump and all that makes it feel “proper”.
After some experimentation I ended up using two simple filters.
First PosterizationFilter (from jme3-effects) with 32 colors and I keep texture filtering on.
And second I implemented the most basic chromatic aberration filter, but I keep it very subtle (it’s hard to notice, look at the chess tiles in the last part of the video).
You can download the game if you want to try, I will update it with these changes no later than this weekend.