I'm not real fond of any class system for modern heroic, or future play. I always feel as if the system is too limiting in the kind of options you can get and does not give you enough of those options.

Look at your own skill set. Simple question: Could you build you with "X" system? If not then that system isn't good enough for a modern or post modern setting. I fear that d20 modern fails the test. Not enough skills points and too few skills to make the grade. And I'm not even mentioning the clunky nature of the class advancement structure.

I'm good with d20 for fantasy play mainly from long use and familiarity. It's an old friend whose flaws I am used to and forgiving of. I don't like it outside of that structure, the flaws become glaring.