First off is the new Nightmare Before Christmas, it looks absolutely amazing in HD, crisp and clear and the contrast between the nearly monochromatic Halloween Town and the over saturated colors of Christmas Town is eye popping. The black light scene with Mr Oogie Boogie torturing "Sandy Claws" looks spectacular.
I compared it with the original letterboxed DVD release and it's not even close, it looks like VHS by comparison.

Next is "That's Entertainment" from 1974 (I II & III are all in the BR collection)
Here's a chance to see some vintage B&W clips as well as 3 strip Technicolor in all it's restored glory and it's dazzling.
The first one is nearly two hours of the best clips from the MGM Musical library, some of the old Busby Berkley stuff is fantastic in HD even in when it's in B&W!