The problem I have seen with Open Source games is not usually with the game itself, but the art work. I wish someday these games would compete with proprietary games on "beauty" as well as functionality.
A difficult proposition when you considered that millions of dollars are poured into proprietary games. Open-source games do not make any significant money, and therefore can not afford to pay artists to spend a lot of time on their product.
The cost argument can not always be made. Millions of dollars are also poured into commercial software. Yet open source alternatives exist that are really good. For example icc vs gcc.
This happened because a lot of computer scientists / engineers donated their time willingly for these projects. My original statement was meant to point out there is a lack of designers in the open source community.
So, where can you sign up as an open source / creative commons artist? There are a lot of great hobby artists, but who will introduce the artists to the projects?