Overall the writing wasn't bad for the most part.
But I have a problem with the tone shift.
This review will be full of negative bias, I hate pointless angst.

The story starts like a slightly depressing but overall happy and funny story for kids, about determination and all that nice stuff.

But, later the action gets muddled, the story is increasingly filled with angst for the sake of angst (at times it feels like it makes no sense plot-wise and the plot gains nothing from it, just angst for the sake of angst)

This culminates with some particularly nasty and sort of cliche character death (which I sort of expected, but that didn't make me hate it any less)

After chapter 138 my enjoyment of this manga fell to 0 and now I feel defiled, dirty and disgusted.
I enjoy stories which fill me with happy feelings, I hate when a story fills me with resentment and urges for bodily harm done to the author.

There's nothing more to it, I simply hate this story now... I don't recommend it, unless you enjoy torturing little imaginary kids and character death.

As much as I'd like to, I'm unable to make myself rate this any higher. I wish I never read this manga, should have stayed with the anime.