If you check out the change log of beta 3, it says that the iPhone 4 lost most of the visual elements, like the parallax, blurred backgrounds and dynamic wallpaper.
Only bugs I can comment on so far is that caller ID still doesn't work on the 4S (besides from calls made from the same provider), and that the subtle shadow added behind app labels only appear when I swipe up on the control center, but when I close control center, the shadow disappears.
Wallpapers section crashes constantly. The fonts are a bit bolder and on a white background, they put a shadow to make it not blend in so much. They removed the .com from the keyboard in safari and a dot is in it's place instead. The progress bar in Safari is thicker and the font is thicker as well. Fonts overall are a bit thicker.
It does seem that the animation from the lock screen to the home screen moves faster. They added a dot on days that you have something planned in calendars in monthly view, but I didn't notice anything in year view. You can now delete a second location in weather app without it crashing. This is all I have seen so far.
I still have the problem where I will open multitasking and close apps, sometimes an app I closed will still be there.....but just the icon. Let's hope springboard crashes less often.
For some reason one of my email accounts now shows an unread message on the ico even though there are no unread messages. Occasionally, it clears briefly then reappears.