Star Wars Galaxies was such a game. It was an earlier sandbox-style MMORPG that let you customize everything, choose your job or playing style, eventually maybe work your way to Jedi if you choose to, and your skill set. Sony Online Entertainment OBLITERATED it, but years later fans reverse-engineered the whole MMORPG and are still in the process of doing so. Last I saw they had a playable recreation of it. Check out www.swgemu.org for more info on the project. You might have to buy an old copy of it on eBay to get it to work.
