I suspect something may be wrong with your X2VGA (have you checked all the dip switch settings?), or you have an unusually discriminating opinion for video game images.
I would agree that "jaggies" are more prevalent in some games, like halo, because the image is so sharp that the anti-aliasing tricks that rely on pixels bleeding into each other don't work.
However, in my opinion, the slight amount of "jagginess" present is more than compensated by the great clarity and edge definition in the whole image. It really helps with sniping, as you can much more easily discern long range objects.
Playing Mame Roms on my xbox via the x2vga is great too. Those old arcade games look really sharp and colorful.
All the people at Halo LAN gatherings who have seen Halo on my x2vga/LCD screen say "wow, that looks so sharp, I gotta get that setup". No one has told me it looks worse than composite.