Many people try open-source games and have great and really nice plans. But there come obstacles. They are divided into 2 groups:
1. Money
You NEED money. You need at least some of them. There is no way to finish even small game without investing some $. Of course assuming you want it released. You need to spend them for domains, hosting, creating company, doing all registrations, paying for artists [as you may get a programmer that will do it for free or % of profits, don't count on artis in that matter, they are also really lazy]. Most projects go down because people cannot scale project to what they can afford. If you want to start a 3D MMORPG from scratch without winning lottery first, you are really wasting your time. I have been in one open-source project like that
2. Management
Even smallest project requires a project leader that can do the job. And that is not an easy task. And it becomes almost impossible task when you do not pay your people, there is almost no way to really motivate them or get them to work on schedule. You need here skills that you won't learn anyway. Not on some useless Management degree on university [you can be Mc Donald's manager after that in best case]. You need to know about wikis, technical documentation, copygight issues, business law, etc etc. Most game projects are led by people that think that making game will be as fun as playing them. But there is not much fun in it, at least not until things are working, which is really the end.
Skills are not a problem - you can learn if you really want. Time too - you will need 10x more than any professionals and you won't be able to keep any schedules anyway. I made some mistakes already
Started with being lead world designer for 3d MMORPG - it was like 8 years ago or more and if it was finished it would be 10x bigger and more complicated than WoW [which did not exist]. We of course were naive enough to not spot problems like that
Later I tried few more things, but really learned that I should scale down my plans. Working on browser-based game now and even here I know I complicated my life way too much.
If you really want smth you should either start with minor role in medium-project [like browser-baser game] or make your own board-game/flash game [like tower defence]. And indie game makings looks more fun than all those corporations anyway. I bet no one here would like to work for EA