CraftWorld!...
Yeah.
Ok, I'm not against Minecraft clones. I love the hell out of Minecraft, but you've got to be able to do something unique with the concept for people to bother. Why would I buy another Minecraft if I already have the original? This one has different lighting and some physics stuff. Ok, great...what does that add to the gameplay? No one is playing Minecraft for its looks, after all.
For example, someone on reddit mentioned a good idea. If you implement physics then take a page out of the LittleBigPlanet design. Add springs, levers, pulleys, rope, pistons, etc that the player can place and manipulate. MC is all about building but you can't do complicated machinery. So...give us the tools to make machinery and now you've got something!