Man, some of your ideas are brilliant, guys. I was just planning to play it alternately for horror (you see the creatures you just slew having their souls tormented), gross humor (something nasty finds your eye and holds onto it as it does nasty things that I can't post due to the Grandma Rule here), or occasionally exposition (you spot a minion of a villain you'll be meeting in a few levels).
But vengeful evil eye, time traveling sentient eye, and dual roaming eyes would be great. In fact, growing up, one of the PCs' uncles fell into the Abyss. Maybe I could do Battlestar Galactica-esque "meanwhile in Uncle Artep's Abyssal torment" vignettes.