If you have seen the images and videos for the S4 and S5 Lollipop ROMs, you know what to expect by now. The general look and feel of the UI is still very much TouchWiz, to the point where most people will find them indistinguishable. There are only minor changes in the UI, most notably in the notification area, but that's pretty much it. Samsung is still sticking to its own UI design and only making minor modification to fit in with the new Material Design of Lollipop.
You can check out the UI in the video below.