I have no problem with mental illness being used as a plot point if it's done tastefully and creatively. X-Men Legacy is a tremendous entertaining read and has really given me an appreciation for a character I had little or no interest in before. But Wanda's entire arc from Disassembled to Uncanny Avengers quite literally went like this.
oh no, kids not real! -> disassemble! -> I warps the realities! -> no more mutants! -> I'm gone! -> I'm back! -> life force! -> oh no, world gonna end! -> go away Namor! -> no more Phoenix! -> I'm sorry for everything...not!
At no point did we ever get her perspective on any of these events or an actual investigation into her psyche, despite these supposedly being the defining moments of her character. The reader never gets any indication why we should care about this woman at all, much less sympathize with her or try and understand her plight. It all just kind of comes and goes and honestly if you weren't familiar with the character before you can't be faulted for just thinking she was never anything more than what she was portrayed as here. And all of this, for what? Because Bendis wanted to break up the Avengers and put Wolverine and Spider-Man on the team instead, and Quesada thought that there were too many mutants so they needed a quick way to get rid of some? And people want to go back and revisit this story again? I will NEVER understand that sentiment.
Which is ultimately the problem.