Things I Liked...

The Monster looked real. Not out of place or crappy 'special effects'.
The idea of Agent Yellow.
The family and all of their differences.
The plot.
The Running Time. Just the right amount.
The comedic factor was overall enjoyable and added to the movie.
The ending. The little girl dying a heroic death or so at least implied. Glad they had the courage to have her die.

Overall. A must watch for this genre.