I can probably live with the Z angle limitation, though I think the allowable angle could be safely increased. What does consistently bug me is the way ships turn. It would be far more realistic and visually appealing if ships had angular momentum. This would stop ships 'jiggling' as you tap left/right, and make for much smoother movement.
It just doesn't seem right that you can go from zero to full turn immediately, especially since other directional movement doesn't do that. It's most pronounced when you go from once direction to another - rather than taking time for the turn to slow down and switch, it's just immediate.