The color palette in Oblivion alone is more vibrant and saturated than the one in Skyrim. Skyrim is a lot cooler (white balancing wise) and greyer in tone, making it feel a little drab compared to the lush greens of Cyrodiil.

At it’s release though, Oblivion was the prettiest in-game forest around.

Edit: Cheydinhal in particular. Such a pretty city. Sadly it’s super fugly in ESO, but it’s absolutely gorgeous in Oblivion.