The style of MC that I love is the whole Towny/loose RPing thing that you see a lot of in multiplayer. We'd build towns, form nations, have little battles, etc. There was local government and little goofy things that weren't taken very seriously, but still a lot of fun. The server had a lot of issues though. Such as the owner being the final word on everything, but not playing the game at all other than to check in occasionally. I set out to create my own server with a similar premise, but sans the issues...but man that is a lot of work to do alone!

I agree, Minecraft worlds unlike some other sandbox games are backwards compatible mostly. You can create a world with the custom presets that is wild, all hills, all diamonds, massive floating islands in the sky, you name it then go back and play them whenever or as often as you like. Single Player still rocks!