Which way would you go if you could become truly evil or good? Since this is skyrim we are talking about it could come with new perks and abilities, maybe a demonic form and powers if you manage to become as evil as possible and the opposite for good characters, heck maybe even somewhat functional wings ( I'm not thinking flying like a dragon, but gliding and slowly descending instead of falling with your arms in the air) I don't see why not add 2 planes outside of oblivion just for it, we'll maybe not lol too much to incorporate then but the rest would be pretty awesome especially for role plays and such.

Well, Vampire and Vampire Lord ability already offer the character certain enhanced evil abilities, like reanimating corpses or devouring health. The lycanthropy of the Companions seems more bestial (ergo neutral) than actually evil. Also, the daedric artifacts that are available give the players vastly increased powers as well.

Not sure what a corresponding Good power would be, or what it would turn the player into in its extreme form (something resembling a fluffy pink Care Bear maybe?)

You know, for all those nice-guy mass murderer Dragonborn