[Captain Kwok]

There's actually a number of differences, first being the inclusion of many stellar phenomena that aren't available elsewhere. This includes Dwarf stars (white, brown, black), functional Supergiants, Neutron stars and Pulsars, plus the fact that many have actually effects that extend beyond just a system ability.

The quadrant selection itself is less developed compared to FQM, which was primarily by design. I put more energy into making the systems themselves more diverse and didn't really want to clutter the quadrant screen with lots of items not having proper descriptions (really a failure of SE:IV's interface).