The lag.

There's way too many features you can't change, which sometimes increase lag. Example: You can't change the graphics texture. It's locked at 16x16x16 graphics. You can't put 8x8x8, or 4x4x4 graphics (which reduce the lag significantly, even more than lowering resolution.) Also, at the top of the screen, there's a texture which shows you which block you're staring at, which is EXTREMELY useless and increases lag. (like, how can you tell me that you can't tell what block you're looking at) You can't hide the chat. You can't change the vertical chunk loading distance. You can't lower the graphics. Can't disable useless features that increase lag. Game is unplayable due to lag. Code optimization should be implemented.