A while back, I used to have a deep hatred for the Zero Series because to me it was a kick in the pants to X fans. It wasn't enough for Capcom to have Zero steal X's spotlight in X's own Series, but then they give him his own series as well? And what of X in the Zero series? He's just a cyber elf. I thought it was very unfair to X fans.
I also thought that because of the Zero series taking place after X, I didn't think X series had enough space to grow - everything would have to follow a certain pattern to fit into the ElF Wars saga. In other words, everything done in the X Series would eventually have to relate to the ElF Wars and thus a set ending for X's saga.
And finally, I detested Zero's newer design.
So, yeah. To me Zero's series was a big pile of fail. Though recently after listening to some Zero series tracks, I realize it's not such a bad series afterall. It's actaully starting to grow back on me.