I like the movie and I liked the ending.

(SPOILER)The monster was able to transfer emotions to and from the kid, who had felt a lot of pain and sorrow and anger in the past few months, and by them knowing each other's pain, the kid was able to tell the monster earnestly and genuinely, symbolically letting the monster of anger and sorrow leave "peacefully."

Remember, monsters are always symboliv of something. In this case, it was the protagonist's anger and sorrow at his mother's death. By feeling the monster's pain, and it feeling his, the monster understood the kid's feeling of pain and sorrow.

"Bad things happen and it's nobody's fault, but you can still live" is a realization he makes himself. The real conflict is his pain, not the monster, imo. They're just resolved the same way.