Overall, I liked A Part to Play. It is a devastatingly sad book, even with the happier moments included. I cried numerous times while reading it and had to walk away at one point so I didn't dissolve into a blubbering mess.
As far as characters, Lucy is a well developed leading character. She has quirks, flaws, and redeeming characteristics. She has been through so much in her short life and becomes a better person because of it. It would have been nice if her friends had known about her issues. It would have shown a stronger side of Lucy that was slightly lacking.
Chris, on the other hand, was fairly one dimensional, even with his almost split personality. He wasn't a very deep character and for someone so central to the story, that was a little disappointing.
I did love Lucy's Mom and Dad made efforts to contact her throughout the school year, even if Lucy rebuked them most of the time.
I want a friend like Isa. :-)