It's really something how they managed to make the series this bad following X4, but they did it. The flaws in this one are somewhat from mechanical issues (like having to game over yourself multiple times before being able to get parts) but mainly it's just that the level design isn't very good here. Some levels are cool (specifically I like Axle the Red's) but a lot of them are just boring. The worst is definitely Duff McWhalen, but it's not like others are off the hook (Skiver) and just in general the most the level design does here is let you move around as X or Zero, which is nice I guess, but it makes me want more.