I think the entire concept and physics of Minecraft just wouldn't work with anything other than blocks. Your primary objective is survival, and after that, to build. It would get very complicated very quickly if everything were normal dimensions. Not to mention all of the technical problems you would have trying to dig into the side of a sloped hill. There would be clipping and tearing issues everywhere. And if Minecraft had a realistic look... It really wouldn't be half as interesting. The main attraction of Minecraft is the creative license you get with it. You're literally able to build ANYTHING and everything you want. No limits. You could make a 1:1 model of the planet Earth and still have room left over. That simply wouldn't be possible with smooth surfaces.