If you are looking to increase the realism of Minecraft, not the graphics but the gameplay, this mod might be interested.
ENVIROMINE 1.7.2 and 1.7.10 is a mod that is responsible for modifying certain aspects of the game, such as physical blocks, which will now be affected by gravity, as well as add new realistic concepts to the game, such as having to collect water to keep hydrated our character.

Detail and Download here : ENVIROMINE Mod

Homepage: Mods for Minecraft