The car layout is identical, unlike Viewliners I and II.
Prior to the current, ongoing cosmetic refresh, the Superliner Is were rehabbed several years ago. They received faux wood paneling on the aisles instead of carpet on the walls (one of the weirder interior design choices of the past), extremely bright "nuclear dawn" LED aisle lighting, much improved redesigned restroom facilities that fit in the same spaces but feel more open. They also retain some original features such as the extremely narrow (like 5"), nearly useless closets instead of a cubby with a strap and hanger on the IIs.
Superliner IIs did not undergo that rehab, retaining their aisle wall carpet, original restroom layouts, dimmer aisle lighting (which I prefer). Since they haven't really been touched since their delivery in the early 1990s, they generally look pretty worn and tatty. Ironically, the older Superliner Is, delivered 1979-80, look much newer. I imagine this is changing with cars that have undergone the cosmetic refresh.
The main exterior spotting feature is Superliner Is have weird looking European designed trucks. Superliner IIs have much more conventional looking trucks. I cannot really describe it, but I knows it when I sees it.