One thing to realize with these kinds of things (and realize that I haven't looked at their website yet, so I may just be talking out of my ass here) is that companies that open-source their defunct games rarely release the content under a similar license. What this means is that you can download and play with the code all you want, but you have to obtain the content (the pretty pictures and maps and whatnot) through some means. I'm pretty sure that's how they did Quake 2, for instance.