i dont know what is missing in 2.5 that 3 has, but 2.5 actually does not look bad at all...
It is running touchwiz 3.0. The only difference on the epic is that one can not edit the bottom apps, move the home screens around, and there is no daily widget app. All of which I don't really care at all about.
It's an android so ay app that I want to open I can simply put on the main home screen, I don't really need to move home screens around, because it doesn't really do anything to improve the experience since their are already 7 different screens I can customize, and the daily widget app which is somewhat cool, can be replaced by three separate widgets: weather, stocks, and news.
I believe that is primarily the only difference between the epic's touchwiz version than the tmobile's vibrant version. However, the epic does run faster than it's counterparts on t mobile and att. For instance there is no lag exiting out on apps by using the home key that is commonly found on the captivate and the vibrant. I'd much rather have a speedy "less customizable" touchwiz than a slower touchwiz experience that really does nothing to improve the experience. In fact by having it slower, it ruins the experience.