DimensionType is not unique per Dimension. See DimensionManager for more details.
Vanilla now has a chunk loading system, so Forge's will need to be deprecated/adapted.
Some things to note:
Netty is screwy so currently can't join single player. @cpw
Crafting has been MAJORY reworked. The current GameRegistry functions are nooped, this is IN THE WORKS.
Just need to move the recipe list to a full class registry, and then re implement the in-code recipe registration.
Also, it IS advised that modders move to JSON, because ideally we'll see a S->C recipe syncing system in 1.13
which would allow servers to have custom recipes.
OreDictionary currently 1/2 works, need to write a better algorithm for replacing ingredients.
Please be patient
Rendering:
A lot of functions got a new float parameter, this is similar to partial ticks, needs more research
Some notes:
Almost all int x, int y, int z parameters have been changed to BlockPos class
ForgeDirection has been removed, replaced by net.minecraft.util.EnumFacing.
All FML classes have moved from packet cpw.mods.fml to net.minecraftforge.fml
Fluid Rendering has been disabled for the time being, to be re-evaulated and a test mod created for it.
Minecraft now uses a Model based system for rendering blocks and Items. The intention is to expand the model format to better suit modder's needed once it is evaulated.
As such, The model loaders from Forge have been removed, to be replaced by expanding vanilla's model format.
Metadata has been extracted out in Minecraft to IBlockState, which holds a list of properties instead of magic number metadata. DO NOT listen to the fearmongering, you can do EVERYTHING with block states you could previously with metadata.
Stencil Bits are disabled entirely by for the main Display, Modders must enable and recreate the FrameBuffer if they wish to use Stencil Bits.
LexManos