Examples? The Last Ayelid King of Nenalata looked exactly like EVERY standard lich in the game, even liches who had never been Elves. Same clothes, same ugly face, same EVERYTHING. Rare, terrible Daedra and monsters looked exactly like their more common counterparts. The Spectres of some rare ancient king. . . looked like every other spectre.
Only with some of the goblin clan chiefs was there any difference at all ( in helmet, for example).
By the Expansions they had at least fixed this a little. Meridia's Daedra, though built on the same core as Xivalia, at least had a specific skin and look.
But my hope is, that in Skyrim, when you encounter a group of rare creatures, or a unique holdover from some earlier age etc. that those NPCs LOOK distinctive. Even if all they do is tweak the skin and hair tones, a secluded gathering of relic Falmer should not look identical to every Altmer in the game. If you encounter some undead Dwemer lich, he should not be identical to the games Draugr Dragon Priests, differntiated by nothing other than a subtitle.