I think everyone forgets that Minecraft's big feature is not its graphics or its gameplay, it's the procedural content generation. Almost anyone could learn to do Minecraft-level graphics in a few weeks, and the level of interactions (combat, crafting, moving things) could be reasonably approximated, too. But its procedural content generation algorithm is quite complex. You're not going to make an algorithm quite as nice as Minecraft's without a lot of research, a lot of hard work, and a lot of tweaking time.
Well, to be honest, this point is also where one could beat Minecraft at its own game. The minecraft devs haven't put emphasis on world exploration in a long time, instead preferring more traditional game features (like "the end").
There are many features notch promised when the project first started that where never acted upon, and there's definitely still demand for those.
