Slick:
While anti-matter (and even dark matter) races would be cool, they can not really be modeled in se4.
Couslee:
There are only so many ways elements can form compounds (all based off of the types of elements you are dealing with). Life on other planets would have to evolve in a similar way as to on earth (in the very beginning stages), or it would not evolve. The evolution of life from primordial oozes is an extremely rare occurence that requires a very specific set of circumstances (noone is fully aware of them all). Only a very small fraction of other planets in the universe could possibly have any form of life evolve on them. Even without knowing all of the factors that contributed to the evolution of life on earth, we can see that there is a very narrow range of conditions in which life can evolve (speaking on a planetary scale, taking other stellar bodies into account and all, not talking about specific climatic regions on the planet and all that). So, any planet that has life evolve on it is going to be fairly similar to earth in many ways.
I have a question for the lot of you:
What other compounds besides O2 do you think could serve the same role that O2 serves for earth-based macroscopic organisms? Why?