It seems that the new fog levels, I don't know if they've changed since 1.1, (w/ out optifine) in (at least) ma sewer it's basically impossible to see over the middle area from one side of the arena unless your computer can handle far render distance (which mine can't)
It's not the brightness level though, Haunted House is dark, but even me, on a macbook can see what's going on.