Don't know if my opinion is worth anything, but I've spent probably 15 minutes total using the S3 display models. All of my phones to date (EVO 3D, EVO 4G LTE) run Sense, so that's what I'm used to. I was able to navigate through the UI, change settings, etc pretty easily. I was pretty impressed, based on the user-input response, video clip previews, shortcuts to common feature settings and the useful info/icons on the notification bar. I only saw two things I didn't like:
1. Folder Creation. It is completely opposite from stock ICS.
2. The on-screen usable area. The screen is nicely sized, but lower row of icons combined with the screen navigation buttons(?), seems to take up too much space.
The only time I ever thought TouchWiz didn't impress me, was when I used it on the Galaxy Tablets. The performance lag was very noticeable and I felt the UI belonged on a phone and not a 10 inch tablet.