I've never liked games where its always daytime and the weather is always clear. They don't feel very realistic and can become boring rather quickly. I'm hoping Fallout Online will have equally long day and night cycles. I'm also hoping for randomly changing weather. Like cloudy skies, rain, fog, dust or sand storms and such. Snow would be a little hard to code.
I'd like to see the time of day/night and weather conditions directly effect the game. During the day cloudy or overcast skies would cut view distance by a small fraction due to less ambient light. Fog or dust storms would cut the distance even more. Rain would lessen visibility a little and also cause characters to move more slowly. Because of slippery pavement or mud. At night the darkness would cut visibility by 1/3. Any weather effects would stack on top of that.
You could lessen the effects of darkness and/or weather. By adding points to some abilities. Perception could give you better eye site and hearing. Agility would make you less likely to slip or get stuck in mud while its raining.
I think that having days, nights and weather would make the game feel more like you're in real world. Where as the same old static environment wouldn't. Thinking that you know anything about MMOs because you play WoW. Is like thinking you're a master chef because you work at McDonalds.