Drak I just wanted to share this mod with you. It looks amazing. And really improves certain survival aspects vanilla minecraft is lacking. Read more :D. It works with server clients or single player so you could do a test run of the mod http://wiki.terrafirmacraft.com/Installation
Its a complete overhaul the TLDR would need a TLDR of the TLDR.
Off the top of my head:
Complete overhual of the tools system, no more punching trees. Hunger and thirst.
Block gravity, cave ins etc.
Seasons, fully fleshed out and world altering, things grow in spring, in winter snow will build up, walking though it will slow you down.
Ore veins are rare and realistic prospecting required to locate.
Detailed metallurgy and forging.
Detailed agriculture with requirement for crop rotations, realistic growth times (ie a full season not one day) same with animal breeding, takes several months of gestation.
Basically makes the game much more involved, complex and ‘realistic’.
Example: Making a bed.
You need to collect sticks from leaves, and rocks from the ground. Make a spear and kill 2 sheep. Knapp yourself a stone knifebalde and combine with stick to make a stone knife. Use the knife to seperate the wool from the rawhide. Find some clay and make a spindle, (clay on stick) use some sticks to light a fire, knapp an axe head and make an axe to cut some logs. Put the logs on the fire and bake the spindle till it is glowing faint red to harden it (heating temperature matters for all things, notably differnet metals). Use the spindle to sping the wool into yarn, then combine the yard to make wool cloth. Split some logs with the axes to make planks, use the planks to create a crafting table then combine the planks and wool to make your bed.
Did I mention that animals dont naturally respawn and that they also have sexes now- so you need to manage them very carefully lest you end up with all males and no females to breed more? (which in itself takes 6-9 months ingame time)
The Ancient World 
Drak I just wanted to share this mod with you. It looks amazing. And really improves certain survival aspects vanilla minecraft is lacking. Read more :D. It works with server clients or single player so you could do a test run of the mod http://wiki.terrafirmacraft.com/Installation
http://terrafirmacraft.com/index.html
Its a complete overhaul the TLDR would need a TLDR of the TLDR.
Off the top of my head:
Complete overhual of the tools system, no more punching trees. Hunger and thirst.
Block gravity, cave ins etc.
Seasons, fully fleshed out and world altering, things grow in spring, in winter snow will build up, walking though it will slow you down.
Ore veins are rare and realistic prospecting required to locate.
Detailed metallurgy and forging.
Detailed agriculture with requirement for crop rotations, realistic growth times (ie a full season not one day) same with animal breeding, takes several months of gestation.
Basically makes the game much more involved, complex and ‘realistic’.
Example: Making a bed.
You need to collect sticks from leaves, and rocks from the ground. Make a spear and kill 2 sheep. Knapp yourself a stone knifebalde and combine with stick to make a stone knife. Use the knife to seperate the wool from the rawhide. Find some clay and make a spindle, (clay on stick) use some sticks to light a fire, knapp an axe head and make an axe to cut some logs. Put the logs on the fire and bake the spindle till it is glowing faint red to harden it (heating temperature matters for all things, notably differnet metals). Use the spindle to sping the wool into yarn, then combine the yard to make wool cloth. Split some logs with the axes to make planks, use the planks to create a crafting table then combine the planks and wool to make your bed.
Did I mention that animals dont naturally respawn and that they also have sexes now- so you need to manage them very carefully lest you end up with all males and no females to breed more? (which in itself takes 6-9 months ingame time)
explains it sort of (taken from a thread)