I was thinking more like liches, phantoms, wraiths, zombies (much like Draugr, I know), and yes, more skeletons and ghosts - but tougher ones.
I just think it would be nice to have more enemy types to fight. Maybe add in a few high level undead boss fights. New undead summons, etc.
When the crypt doors creek and the tombstones quake
Spooks come out for a singing wake
Happy haunts materialize
And begin to vocalize
Grim grinnin' ghosts come out to socialize!
I do want more spirits and supernatural stuff to be brought to Skyrim. Wraiths, phantoms, and banshees would be especially welcome in my mind.