ok, three points (I think, I may ramble. . )
First, you're right, it would be very difficult to organize a project that competes on a commercial scale (especially the development time frame) in categories like FPS, RPG, MMORG. . .
Where I think there is some originality in OSS games is smaller (mostly 2D projects)
Second (and to illustrate the first) I have actually developed a game in the past year and a half, which I think *is* fairly original. Ok, I admit I did borrow the basic idea. . but from a novel (Ender's Game specifically). It is a 2d shooter, with no gravity called Balder2d. If you're running Dapper, you should be able to just go
to make sure you have all the dependencies, and then grab the zip file for
sudo apt-get install libsdl-image1.2 libsdl-mixer1.2 libsdl-gfx1.2-4 libboost-filesystem1.33.1 libguichan0
(depending on your system), unzip and run ./balder2d (it's in the bin folder, please tell me if this doesn't work!).
So now that my shameless self promotion bit is done, I come to my third point. Funding. As has been pointed out in this thread, the traditional ways in which OSS makes sense for commercial development (ie service based) just doesn't apply to games. So it occurred to me during my local NPR station's bi-annual fund drive, maybe it's possible to do something like that for open source game development? I guess it's *sort of* how cedega is working, but they are not developing original games, and you still have to pay to buy those games anyway. But do you think it would be possible to use the membership model, collect membership pledges, and when you have enough you hire a team of developers, or even some commercial company, to produce the game, with the condition that it will be open source? That way you get professional game developers being payed to write open source games. It's an exciting prospect if it can work.