It has better brakes, a MUCH more user friendly GUI, the option to choose between 5 preset timing profiles and two user customizable software settings, and a smoother overall feel. The first throttle profile is the new spec profile which includes no to timing or turbo and flashes an LED at neutral to ID it. I really liked the brakes as well as the GUI, but I found the smoothness most useful. I copied my 203 settings over to my sedan and it felt a little less punchy. I thought I would try the current limiter option too as they said it had been improved and most people could limit it to 80% and not even see a difference in lap times. I went out and ran like that and was surprised. The motor was a lot cooler, and the car was very easy to drive with lap times as fast or faster than with 203.
Here's the official release info...
http://www.teamtekin.com/hotwire/vegas/ ... -notes.pdf