Over the past couple weeks I've been poking at the physics code. When I started, it was some of the gnarliest looking spaghetti I'd ever seen. I like to think it's a bit cleaner now, and I've addressed some movement issues that have always bothered be with Quake2.
Improved stair jumping; players never get stopped dead in their tracks or shot out sideways from strafe jumping up stairs.
New soft velocity clamp and small air friction prevents players from attaining absurdly high horizontal velocities from strafe jumping.
Note that horizontal jump pads still work as expected, allowing the player to be explicitly pushed at high velocities.
Fixed "water skiing" movement where players can basically skate across the surface of water.
Improved water entry and exit logic and control.
Improved ladder detection.
Increased air acceleration for low-speed jumps, allowing players to negotiate jumping around corners and things.
Improved ground detection logic, allowing for triple jumps and fast ramp jumps previously not possible.
Here's a YouTube video showing off some of these features: