Great ideas! Now turn them realistic. Your best bet is to make a small-scale game that is really addictive, not go out for the big-time and hope it turns out well. I can see one small "world" where the player can do what they please, but make it cool like a seamless world, like a tiny little globe sort of thing. Be choosy about what's dynamic, determine what exactly the player's *verbage* consists of. That is, what exactly will the player be able to do?
Get a whole list of for instance: Walk,Run,Jump,Strafe,Cut Down Trees, Mine Gold, Slash Sword,etc...etc... from that list, you can work on each feature, and keep adding features to make it more and more dynamic. But think small-scale! Tetris is still one of the most popular games in the world, even thought it is considered one of the most simple. After all, if you can get the small stuff down, who says you can't keep adding on? IDK if that was clear enough, but I say take that ambition and narrow down where you're aiming, so that you can really hit the bullseye.