Lightning, for certain. It's always been a key component in the atmosphere of each game in the series. The dark, lonely feeling in Arena/Daggerfall to the earthy, stark colors of Morrowind to the lush, dreamy colors of Oblivion. At the same time, I think it's also where Bethesda needs to make the most improvements. Less excessive ambient lighting, please! I liked how "tight" things felt in Morrowind's interiors, because there weren't dramatic reflections and blue tints everywhere I went.
Music is the most important factor in audio, for me - I'm hoping we see multiple tracks, per location, time of day, and weather. The playlist system used in every game since Morrowind can only do so much.
Hey thats a realy good idea. Have the Auio change based on the weather. Sort of happy fun time songs when its sunny, dark brooding music when its stormy, and soft relaxing music when its raining. That'd be great.
I loved listening to the music at the fishing hole in Twilight Princess. esp when it rained.
You can get away with skimping on lighting and model complexity by just making those textures look so darn pretty.
No, no you cant. Not after playing Stalker.
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