Minecraft wiki entry for Dimension, associated text: Sleeping in a bed skips the night and sets spawn point (explodes when used in other dimensions).
The most biomes of any dimension.
Surface and underground biomes.
Oceans containing water.
The most amount of ores.
Many naturally generated structures.
The most types of mobs.
A daylight cycle.
Weather.
A total vertical height of 384 blocks, as opposed to 256 blocks for other dimensions.