1. EnviroMine:

The top number is your body temperature. The thermometer next to is animated, and displays if your current situation is too hot or too cold. Overheating leads to Heatstroke, where as being cold lead to Hypothermia. If the thermometer is full and red, leave the proximity of torches, drink some cool water or change your armor. Likewise, seek shelter and fire if it's too cold.

The bottom number is your hydration. If it reaches 0, you'll quickly lose health and die. You can drink water from water source blocks (it consumes the block) or by gathering water into glass bottles. Be careful where you drink from though, since salt water and dirty water can poison you. Throwing a glass bottle with either into a furnace will give you clean water you can drink safely.

While difficult to make out the slots in the Sphax texture pack due to the darkness, these are 6 extra weapon slots (3 on each side). You can access them by clicking the BG in your inventory, where you can equip 3 different sets of weapons. While playing, you can press R (or whatever you set the key to) in order to swap between your regular toolbar and these weapon bars.

Automatic healing is disabled in Hinterfall. The only way to heal yourself is while eating food (very small amounts) or using a healing potion or golden apple. Your maximum health is also half of what it normally is in Vanilla Minecraft, only 5 full hearts. You can increase your maximum health by collecting Heart Fragments from mobs and crafting Hearts. You can gain another 5 full hearts, however you'll lose all of them if you die.

Not shown in the screenshot is golden hearts that represents Natural Absorption. These count as health points that recharge automatically after a little while. You start the game with 1 point of Natural Absorption, and you lose 1 point each time you die. You can use Rose Gold to craft a Book of Absorption, which can be used for 30 experience levels to give you a new point of Natural Absorption. You can accumulate a max of 10 points of Natural Absorption. All together, with a full set of health points from Heart Fragments and a full set of Natural Absorption a player can accumulate the equivilant to 20 full hearts of health.

Now you can actually visualize how much hunger your activities are consuming. You can also see exactly how much each Satiation you have. These Vanilla mechanics are simply no longer hidden.

Keep in mind, food now spoils over time. Build Freezers or Eskies to prolong perishables. Also, eating the same type of food too often will lower how much nutrition you gain from it. You can no longer survive on only one type of cusine and must have a healthy variety to remain effective. Spoilage and nutritional value are both listed in the item's tooltip.

The top number on this side of the screen is your Sanity. Being in total darkness, near enemy monsters or near death will lower your Sanity. Once your Sanity is gone, you will be unable to jump up 1 block high and will constantly hear enemy monsters whether they are there or not. Avoid it if possible.

The bottom number is Air Quality. While digging deep underground, smoke from torches will cause the air quality to diminish. Either plant flowers and greenery to improve the air quality as you mine, or craft gas masks to explore the depths without worry.

Several mods give notifications of status effects, from Heatstroke to simply announcing when you are Injured or Dying. Most of these notifications have been customized to show on the top left of the screen. Pay attention to that area.