The Good: Costumes, cinematography, all the key characters returning, Maggie Smith
The Bad: Plot, overacting, and LOUD/soft score.
Except for Edith's, the storylines were so bad there was no way these talented actors could save the movie. The writing tried too hard, the drama way too forced (meeting in the cellar to stage a coup?), and everything ended up excruciatingly sappy. The series was not this way, which is why it was so disappointing to have the movie fall prey to these common traps.
But what nearly had me turn off the movie was the music and the leveling. The music was very in-your-face and it went from LOUD AS ALL GET OUT music to soft conversation then immediately to LOUD music again. Over and over, especially at the end. Beyond irritating.