I don't know why it took me so long to read this Stephen King classic. It is a great story! And quite thought-provoking if you know anything about MKUltra. 
While the characters weren't the best developed, the story is definitely memorable.

Charlie seemed more like a 10 year old, than an 8 year old, but then she also isn't an ordinary kid, so that may have an affect. 
I wish there was a little more about Andy (the dad)'s inner life. Or more talk of the mother. A child that JUST lost her mother would probably think of her more... 
I liked the characters plotlines of Pynchot and Cap. The ricochet was beautifully done in my opinion. 
Rainbird was probably the most fleshed out, in motive, background, etc etc. I did not like him at all (which isn't bad, as he is a villain). He just made me so angry. 
The ending felt so abrupt though. The shop agents walking in on the Manders just having found the note. Going off the previous pattern of detailed explanation s of what is happening, it felt like an odd choice to just leave it at that.
As for Charlie. Love that she went to the Rolling Stone, but I wish there would've been at least a newspaper cutout at the end or something. I get leaving it out in the open and open endings, but aah I wanna know!