'X' was a sad attempt at a past-it band desperatly trying to sound relevant.
Bon Jovi managed it by gradually changing thier sound, progessing and maturing with the years, whilst sticking with the same key principles and song themes.
Def Leppard hadn't progressed at all when it comes to song-writing and production, they were just rehashing Pyromania. It seemed they had finally wised-up when 'X' came along, but it was a case of 'too little, too late'.

They've still got it live though (bar Joe's voice), i'll give them that.