About the content - we surely didn't do it all in just this small time. The character model is from alienheretic (he has a thread about it and three others in the user contributions section), the textures mostly aren't made by us too. We both hate the fact that everyone makes his own content for the game, which results in enormously long development times and further, in another unfinished project. So we've started where others have already done something (and are willing to give it away), made our own adjustments (own sky, some tweaks here and there, own environment models etc.) and then we've started doing the levels and the code.
If we had made everything ourselves, we woulnd't even have half as much progress as we have now. And don't worry, everyone will get his credits