The story telling and more gameplay advancements, i would change X4 ,X5 , X6 , X7 and X8 because i think after X4 things started to get confusing a little bit , i think i would rather change the levels of X4,X5,X6 a bit because most of them feel recycled with bad CG and don`t stand out like they do in the Super Famicon/SNES X games and i think X7 should have had more time to be developed because it wasnt good but it wasnt as bad as people think , if they polished it more , it would've been something amazing if it had more time , the idea was actually pretty cool to have a 2D and 3D battlefield. I wish that X8 was like X7 but better and improved but they were scared from the fans being angry about X7, but if they took the risk to make X8 like X7 but better then that would be really amazing since then the X series could have advanced more further and i agree with the voice acting , they should have dual audio.