Meh, I'm kind of pissed off by Inafune's blatant bias towards Zero, to be honest. I think that's primarily what ruined the series. He just HAD to end the X series so he could prance off to Inti-Creates and make a series about his favorite character ever.
Just because Zero wasn't the main character, doesn't mean he couldn't play a main part in the plot. I actually thought X4 giving you the option to play as both was really cool. Unfortunately, X's storyline got shafted in favor of Zero's anyway ~_~
Seriously, though. What a blatant fanboy he is >.>