While I enjoy Warriors of Mars, I find it to be just a bit too vague. And on specifics it says "refer to this obscure out of print zine from 2001" I'm talking about the Psion for example.
I do think it is a good outline that a creative DM could flesh out, I just like to have a little more to work with.
The good thing is it made me track down an issue of OD&Dities I didn't have; Issue #4 with the psionicist class. Now I have to roll up my sleeves and convert it into a class I can actually use in my games.