Creating Minecraft is a lot of work, but creating something that generates psuedorandom worlds and lets you walk around them is a feasible couple-of-months-of-spare-time sort of project, assuming general programming competence but not assuming any particular skills in computer graphics. Odds are good you can find someone blog posting about it in your favorite language if you look. I've seen a number of them. If you cheat and use the Minecraft textures it looks a lot like early Minecraft too.